content/browser/renderer_host/input/gesture_event_queue.cc - chromium/src.git - Git at Google

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #include "content/browser/renderer_host/input/gesture_event_queue.h"

 #include "base/auto_reset.h"
 #include "base/trace_event/trace_event.h"
 #include "content/browser/renderer_host/input/touchpad_tap_suppression_controller.h"
 #include "content/browser/renderer_host/input/touchscreen_tap_suppression_controller.h"
 #include "ui/events/blink/blink_features.h"
 #include "ui/events/blink/web_input_event_traits.h"

 using blink::WebGestureEvent;
 using blink::WebInputEvent;

 namespace content {

 GestureEventQueue::GestureEventWithLatencyInfoAndAckState::
     GestureEventWithLatencyInfoAndAckState(
         const GestureEventWithLatencyInfo& event)
     : GestureEventWithLatencyInfo(event) {}

 GestureEventQueue::Config::Config() {
 }

 GestureEventQueue::GestureEventQueue(
     GestureEventQueueClient* client,
     FlingControllerEventSenderClient* fling_event_sender_client,
     FlingControllerSchedulerClient* fling_scheduler_client,
     const Config& config)
     : client_(client),
       fling_in_progress_(false),
       scrolling_in_progress_(false),
       ignore_next_ack_(false),
       allow_multiple_inflight_events_(
           base::FeatureList::IsEnabled(features::kVsyncAlignedInputEvents)),
       debounce_interval_(config.debounce_interval),
       fling_controller_(this,
                         fling_event_sender_client,
                         fling_scheduler_client,
                         config.fling_config) {
   DCHECK(client);
   DCHECK(fling_event_sender_client);
   DCHECK(fling_scheduler_client);
 }

 GestureEventQueue::~GestureEventQueue() { }

 bool GestureEventQueue::DebounceOrQueueEvent(
     const GestureEventWithLatencyInfo& gesture_event) {
   // GFS should have been filtered in FlingControllerFilterEvent.
   DCHECK_NE(gesture_event.event.GetType(), WebInputEvent::kGestureFlingStart);
   if (!ShouldForwardForBounceReduction(gesture_event))
     return false;

   QueueAndForwardIfNecessary(gesture_event);
   return true;
 }

 bool GestureEventQueue::FlingControllerFilterEvent(
     const GestureEventWithLatencyInfo& gesture_event) {
   TRACE_EVENT0("input", "GestureEventQueue::QueueEvent");
   if (fling_controller_.FilterGestureEvent(gesture_event))
     return true;

   // fling_controller_ is in charge of handling GFS events and the events are
   // not sent to the renderer, the controller processes the fling and generates
   // fling progress events (wheel events for touchpad and GSU events for
   // touchscreen and autoscroll) which are handled normally.
   if (gesture_event.event.GetType() == WebInputEvent::kGestureFlingStart) {
     fling_controller_.ProcessGestureFlingStart(gesture_event);
     fling_in_progress_ = true;
     return true;
   }

   // If the GestureFlingStart event is processed by the fling_controller_, the
   // GestureFlingCancel event should be the same.
   if (gesture_event.event.GetType() == WebInputEvent::kGestureFlingCancel) {
     fling_controller_.ProcessGestureFlingCancel(gesture_event);
     fling_in_progress_ = false;
     return true;
   }

   return false;
 }

 void GestureEventQueue::StopFling() {
   fling_in_progress_ = false;
   fling_controller_.StopFling();
 }

 bool GestureEventQueue::FlingCancellationIsDeferred() const {
   return fling_controller_.FlingCancellationIsDeferred();
 }

 gfx::Vector2dF GestureEventQueue::CurrentFlingVelocity() const {
   return fling_controller_.CurrentFlingVelocity();
 }

 bool GestureEventQueue::ShouldDiscardFlingCancelEvent(
     const GestureEventWithLatencyInfo& gesture_event) const {
   // When the GFS is processed by the fling_controller_ the controller handles
   // GFC filtering as well.
   DCHECK(!(fling_controller_.fling_in_progress()));

   if (coalesced_gesture_events_.empty() && fling_in_progress_)
     return false;
   GestureQueueWithAckState::const_reverse_iterator it =
       coalesced_gesture_events_.rbegin();
   while (it != coalesced_gesture_events_.rend()) {
     if (it->event.GetType() == WebInputEvent::kGestureFlingStart)
       return false;
     if (it->event.GetType() == WebInputEvent::kGestureFlingCancel)
       return true;
     it++;
   }
   return true;
 }

 bool GestureEventQueue::ShouldForwardForBounceReduction(
     const GestureEventWithLatencyInfo& gesture_event) {
   if (debounce_interval_ <= base::TimeDelta())
     return true;

   // Don't debounce any gesture events while a fling is in progress on the
   // browser side. A GSE event in this case ends fling progress and it shouldn't
   // get cancelled by its next GSB event.
   if (fling_controller_.fling_in_progress())
     return true;

   switch (gesture_event.event.GetType()) {
     case WebInputEvent::kGestureScrollUpdate:
       if (!scrolling_in_progress_) {
         debounce_deferring_timer_.Start(
             FROM_HERE,
             debounce_interval_,
             this,
             &GestureEventQueue::SendScrollEndingEventsNow);
       } else {
         // Extend the bounce interval.
         debounce_deferring_timer_.Reset();
       }
       scrolling_in_progress_ = true;
       debouncing_deferral_queue_.clear();
       return true;

     case WebInputEvent::kGestureFlingStart:
       // GestureFlingStart shouldn't be debounced because it is a discrete event
       // signalling the end of a scroll
       debounce_deferring_timer_.Stop();
       GestureEventQueue::SendScrollEndingEventsNow();
       return true;

     case WebInputEvent::kGesturePinchBegin:
     case WebInputEvent::kGesturePinchEnd:
     case WebInputEvent::kGesturePinchUpdate:
       // TODO(rjkroege): Debounce pinch (http://crbug.com/147647)
       return true;
     default:
       if (scrolling_in_progress_) {
         debouncing_deferral_queue_.push_back(gesture_event);
         return false;
       }
       return true;
   }
 }

 void GestureEventQueue::QueueAndForwardIfNecessary(
     const GestureEventWithLatencyInfo& gesture_event) {
   if (allow_multiple_inflight_events_) {
     // Event coalescing should be handled in compositor thread event queue.
     if (gesture_event.event.GetType() == WebInputEvent::kGestureFlingCancel)
       fling_in_progress_ = false;
     else if (gesture_event.event.GetType() == WebInputEvent::kGestureFlingStart)
       fling_in_progress_ = true;
     coalesced_gesture_events_.push_back(gesture_event);
     client_->SendGestureEventImmediately(gesture_event);
     return;
   }

   switch (gesture_event.event.GetType()) {
     case WebInputEvent::kGestureFlingCancel:
       fling_in_progress_ = false;
       break;
     case WebInputEvent::kGestureFlingStart:
       fling_in_progress_ = true;
       break;
     case WebInputEvent::kGesturePinchUpdate:
     case WebInputEvent::kGestureScrollUpdate:
       QueueScrollOrPinchAndForwardIfNecessary(gesture_event);
       return;
     case WebInputEvent::kGestureScrollBegin:
       if (OnScrollBegin(gesture_event))
         return;
       break;
     default:
       break;
   }

   coalesced_gesture_events_.push_back(gesture_event);
   if (coalesced_gesture_events_.size() == 1)
     client_->SendGestureEventImmediately(gesture_event);
 }

 bool GestureEventQueue::OnScrollBegin(
     const GestureEventWithLatencyInfo& gesture_event) {
   // If a synthetic scroll begin is encountered, it can cancel out a previous
   // synthetic scroll end. This allows a later gesture scroll update to coalesce
   // with the previous one. crbug.com/607340.
   bool synthetic = gesture_event.event.data.scroll_begin.synthetic;
   bool have_unsent_events =
       EventsInFlightCount() < coalesced_gesture_events_.size();
   if (synthetic && have_unsent_events) {
     GestureEventWithLatencyInfo* last_event = &coalesced_gesture_events_.back();
     if (last_event->event.GetType() == WebInputEvent::kGestureScrollEnd &&
         last_event->event.data.scroll_end.synthetic) {
       coalesced_gesture_events_.pop_back();
       return true;
     }
   }
   return false;
 }

 void GestureEventQueue::ProcessGestureAck(InputEventAckSource ack_source,
                                           InputEventAckState ack_result,
                                           WebInputEvent::Type type,
                                           const ui::LatencyInfo& latency) {
   TRACE_EVENT0("input", "GestureEventQueue::ProcessGestureAck");

   if (coalesced_gesture_events_.empty()) {
     DLOG(ERROR) << "Received unexpected ACK for event type " << type;
     return;
   }

   if (!allow_multiple_inflight_events_) {
     LegacyProcessGestureAck(ack_source, ack_result, type, latency);
     return;
   }

   // ACKs could come back out of order. We want to cache them to restore the
   // original order.
   for (auto& outstanding_event : coalesced_gesture_events_) {
     if (outstanding_event.ack_state() != INPUT_EVENT_ACK_STATE_UNKNOWN)
       continue;
     if (outstanding_event.event.GetType() == type) {
       outstanding_event.latency.AddNewLatencyFrom(latency);
       outstanding_event.set_ack_info(ack_source, ack_result);
       break;
     }
   }

   AckCompletedEvents();
 }

 void GestureEventQueue::AckCompletedEvents() {
   // Don't allow re-entrancy into this method otherwise
   // the ordering of acks won't be preserved.
   if (processing_acks_)
     return;
   base::AutoReset<bool> process_acks(&processing_acks_, true);
   while (!coalesced_gesture_events_.empty()) {
     auto iter = coalesced_gesture_events_.begin();
     if (iter->ack_state() == INPUT_EVENT_ACK_STATE_UNKNOWN)
       break;
     GestureEventWithLatencyInfoAndAckState event = *iter;
     coalesced_gesture_events_.erase(iter);
     AckGestureEventToClient(event, event.ack_source(), event.ack_state());
   }
 }

 void GestureEventQueue::AckGestureEventToClient(
     const GestureEventWithLatencyInfo& event_with_latency,
     InputEventAckSource ack_source,
     InputEventAckState ack_result) {
   DCHECK(allow_multiple_inflight_events_);

   // Ack'ing an event may enqueue additional gesture events.  By ack'ing the
   // event before the forwarding of queued events below, such additional events
   // can be coalesced with existing queued events prior to dispatch.
   client_->OnGestureEventAck(event_with_latency, ack_source, ack_result);

   fling_controller_.OnGestureEventAck(event_with_latency, ack_result);
 }

 void GestureEventQueue::LegacyProcessGestureAck(
     InputEventAckSource ack_source,
     InputEventAckState ack_result,
     WebInputEvent::Type type,
     const ui::LatencyInfo& latency) {
   DCHECK(!allow_multiple_inflight_events_);

   // Events are forwarded one-by-one.
   // It's possible that the ack for the second event in an in-flight,
   // coalesced Gesture{Scroll,Pinch}Update pair is received prior to the first
   // event ack.
   size_t event_index = 0;
   if (ignore_next_ack_ && coalesced_gesture_events_.size() > 1 &&
       coalesced_gesture_events_[0].event.GetType() != type &&
       coalesced_gesture_events_[1].event.GetType() == type) {
     event_index = 1;
   }

   GestureEventWithLatencyInfo event_with_latency =
       coalesced_gesture_events_[event_index];
   DCHECK_EQ(event_with_latency.event.GetType(), type);
   event_with_latency.latency.AddNewLatencyFrom(latency);

   // Ack'ing an event may enqueue additional gesture events.  By ack'ing the
   // event before the forwarding of queued events below, such additional events
   // can be coalesced with existing queued events prior to dispatch.
   client_->OnGestureEventAck(event_with_latency, ack_source, ack_result);

   fling_controller_.OnGestureEventAck(event_with_latency, ack_result);

   DCHECK_LT(event_index, coalesced_gesture_events_.size());
   coalesced_gesture_events_.erase(coalesced_gesture_events_.begin() +
                                   event_index);

   if (ignore_next_ack_) {
     ignore_next_ack_ = false;
     return;
   }

   if (coalesced_gesture_events_.empty())
     return;

   const GestureEventWithLatencyInfo& first_gesture_event =
       coalesced_gesture_events_.front();

   // Check for the coupled GesturePinchUpdate before sending either event,
   // handling the case where the first GestureScrollUpdate ack is synchronous.
   GestureEventWithLatencyInfo second_gesture_event;
   if (first_gesture_event.event.GetType() ==
           WebInputEvent::kGestureScrollUpdate &&
       coalesced_gesture_events_.size() > 1 &&
       coalesced_gesture_events_[1].event.GetType() ==
           WebInputEvent::kGesturePinchUpdate) {
     second_gesture_event = coalesced_gesture_events_[1];
     ignore_next_ack_ = true;
   }

   client_->SendGestureEventImmediately(first_gesture_event);
   if (second_gesture_event.event.GetType() != WebInputEvent::kUndefined)
     client_->SendGestureEventImmediately(second_gesture_event);
 }

 TouchpadTapSuppressionController*
     GestureEventQueue::GetTouchpadTapSuppressionController() {
   return fling_controller_.GetTouchpadTapSuppressionController();
 }

 void GestureEventQueue::FlingHasBeenHalted() {
   fling_in_progress_ = false;
 }

 void GestureEventQueue::ForwardGestureEvent(
     const GestureEventWithLatencyInfo& gesture_event) {
   QueueAndForwardIfNecessary(gesture_event);
 }

 void GestureEventQueue::SendScrollEndingEventsNow() {
   scrolling_in_progress_ = false;
   if (debouncing_deferral_queue_.empty())
     return;
   GestureQueue debouncing_deferral_queue;
   debouncing_deferral_queue.swap(debouncing_deferral_queue_);
   for (GestureQueue::const_iterator it = debouncing_deferral_queue.begin();
        it != debouncing_deferral_queue.end(); it++) {
     if (!fling_controller_.FilterGestureEvent(*it)) {
       QueueAndForwardIfNecessary(*it);
     }
   }
 }

 void GestureEventQueue::QueueScrollOrPinchAndForwardIfNecessary(
     const GestureEventWithLatencyInfo& gesture_event) {
   DCHECK_GE(coalesced_gesture_events_.size(), EventsInFlightCount());
   const size_t unsent_events_count =
       coalesced_gesture_events_.size() - EventsInFlightCount();
   if (!unsent_events_count) {
     coalesced_gesture_events_.push_back(gesture_event);
     if (coalesced_gesture_events_.size() == 1) {
       client_->SendGestureEventImmediately(gesture_event);
     } else if (coalesced_gesture_events_.size() == 2) {
       DCHECK(!ignore_next_ack_);
       // If there is an in-flight scroll, the new pinch can be forwarded
       // immediately, avoiding a potential frame delay between the two
       // (similarly for an in-flight pinch with a new scroll).
       const GestureEventWithLatencyInfo& first_event =
           coalesced_gesture_events_.front();
       if (gesture_event.event.GetType() != first_event.event.GetType() &&
           ui::IsCompatibleScrollorPinch(gesture_event.event,
                                         first_event.event)) {
         ignore_next_ack_ = true;
         client_->SendGestureEventImmediately(gesture_event);
       }
     }
     return;
   }

   GestureEventWithLatencyInfo* last_event = &coalesced_gesture_events_.back();
   if (last_event->CanCoalesceWith(gesture_event)) {
     last_event->CoalesceWith(gesture_event);
     return;
   }

   if (!ui::IsCompatibleScrollorPinch(gesture_event.event, last_event->event)) {
     coalesced_gesture_events_.push_back(gesture_event);
     return;
   }

   // Extract the last event in queue.
   blink::WebGestureEvent last_gesture_event =
       coalesced_gesture_events_.back().event;
   DCHECK_LE(coalesced_gesture_events_.back().latency.trace_id(),
             gesture_event.latency.trace_id());
   ui::LatencyInfo oldest_latency = coalesced_gesture_events_.back().latency;
   oldest_latency.set_coalesced();
   coalesced_gesture_events_.pop_back();

   // Extract the second last event in queue.
   ui::WebScopedInputEvent second_last_gesture_event = nullptr;
   if (unsent_events_count > 1 &&
       ui::IsCompatibleScrollorPinch(gesture_event.event,
                                     coalesced_gesture_events_.back().event)) {
     second_last_gesture_event =
         ui::WebInputEventTraits::Clone(coalesced_gesture_events_.back().event);
     DCHECK_LE(coalesced_gesture_events_.back().latency.trace_id(),
               oldest_latency.trace_id());
     oldest_latency = coalesced_gesture_events_.back().latency;
     oldest_latency.set_coalesced();
     coalesced_gesture_events_.pop_back();
   }

   std::pair<blink::WebGestureEvent, blink::WebGestureEvent> coalesced_events =
       ui::CoalesceScrollAndPinch(
           second_last_gesture_event
               ? &ui::ToWebGestureEvent(*second_last_gesture_event)
               : nullptr,
           last_gesture_event, gesture_event.event);

   GestureEventWithLatencyInfo scroll_event;
   scroll_event.event = coalesced_events.first;
   scroll_event.latency = oldest_latency;

   GestureEventWithLatencyInfo pinch_event;
   pinch_event.event = coalesced_events.second;
   pinch_event.latency = oldest_latency;

   coalesced_gesture_events_.push_back(scroll_event);
   coalesced_gesture_events_.push_back(pinch_event);
 }

 size_t GestureEventQueue::EventsInFlightCount() const {
   if (allow_multiple_inflight_events_) {
     // Currently unused, can be removed if compositor event queue was enabled by
     // default.
     NOTREACHED();
     return coalesced_gesture_events_.size();
   }

   if (coalesced_gesture_events_.empty())
     return 0;

   if (!ignore_next_ack_)
     return 1;

   DCHECK_GT(coalesced_gesture_events_.size(), 1U);
   return 2;
 }

 }  // namespace content
	// Copyright 2014 The Chromium Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	#include "content/browser/renderer_host/input/gesture_event_queue.h"

	#include "base/auto_reset.h"
	#include "base/trace_event/trace_event.h"
	#include "content/browser/renderer_host/input/touchpad_tap_suppression_controller.h"
	#include "content/browser/renderer_host/input/touchscreen_tap_suppression_controller.h"
	#include "ui/events/blink/blink_features.h"
	#include "ui/events/blink/web_input_event_traits.h"

	using blink::WebGestureEvent;
	using blink::WebInputEvent;

	namespace content {

	GestureEventQueue::GestureEventWithLatencyInfoAndAckState::
	GestureEventWithLatencyInfoAndAckState(
	const GestureEventWithLatencyInfo& event)
	: GestureEventWithLatencyInfo(event) {}

	GestureEventQueue::Config::Config() {
	}

	GestureEventQueue::GestureEventQueue(
	GestureEventQueueClient* client,
	FlingControllerEventSenderClient* fling_event_sender_client,
	FlingControllerSchedulerClient* fling_scheduler_client,
	const Config& config)
	: client_(client),
	fling_in_progress_(false),
	scrolling_in_progress_(false),
	ignore_next_ack_(false),
	allow_multiple_inflight_events_(
	base::FeatureList::IsEnabled(features::kVsyncAlignedInputEvents)),
	debounce_interval_(config.debounce_interval),
	fling_controller_(this,
	fling_event_sender_client,
	fling_scheduler_client,
	config.fling_config) {
	DCHECK(client);
	DCHECK(fling_event_sender_client);
	DCHECK(fling_scheduler_client);
	}

	GestureEventQueue::~GestureEventQueue() { }

	bool GestureEventQueue::DebounceOrQueueEvent(
	const GestureEventWithLatencyInfo& gesture_event) {
	// GFS should have been filtered in FlingControllerFilterEvent.
	DCHECK_NE(gesture_event.event.GetType(), WebInputEvent::kGestureFlingStart);
	if (!ShouldForwardForBounceReduction(gesture_event))
	return false;

	QueueAndForwardIfNecessary(gesture_event);
	return true;
	}

	bool GestureEventQueue::FlingControllerFilterEvent(
	const GestureEventWithLatencyInfo& gesture_event) {
	TRACE_EVENT0("input", "GestureEventQueue::QueueEvent");
	if (fling_controller_.FilterGestureEvent(gesture_event))
	return true;

	// fling_controller_ is in charge of handling GFS events and the events are
	// not sent to the renderer, the controller processes the fling and generates
	// fling progress events (wheel events for touchpad and GSU events for
	// touchscreen and autoscroll) which are handled normally.
	if (gesture_event.event.GetType() == WebInputEvent::kGestureFlingStart) {
	fling_controller_.ProcessGestureFlingStart(gesture_event);
	fling_in_progress_ = true;
	return true;
	}

	// If the GestureFlingStart event is processed by the fling_controller_, the
	// GestureFlingCancel event should be the same.
	if (gesture_event.event.GetType() == WebInputEvent::kGestureFlingCancel) {
	fling_controller_.ProcessGestureFlingCancel(gesture_event);
	fling_in_progress_ = false;
	return true;
	}

	return false;
	}

	void GestureEventQueue::StopFling() {
	fling_in_progress_ = false;
	fling_controller_.StopFling();
	}

	bool GestureEventQueue::FlingCancellationIsDeferred() const {
	return fling_controller_.FlingCancellationIsDeferred();
	}

	gfx::Vector2dF GestureEventQueue::CurrentFlingVelocity() const {
	return fling_controller_.CurrentFlingVelocity();
	}

	bool GestureEventQueue::ShouldDiscardFlingCancelEvent(
	const GestureEventWithLatencyInfo& gesture_event) const {
	// When the GFS is processed by the fling_controller_ the controller handles
	// GFC filtering as well.
	DCHECK(!(fling_controller_.fling_in_progress()));

	if (coalesced_gesture_events_.empty() && fling_in_progress_)
	return false;
	GestureQueueWithAckState::const_reverse_iterator it =
	coalesced_gesture_events_.rbegin();
	while (it != coalesced_gesture_events_.rend()) {
	if (it->event.GetType() == WebInputEvent::kGestureFlingStart)
	return false;
	if (it->event.GetType() == WebInputEvent::kGestureFlingCancel)
	return true;
	it++;
	}
	return true;
	}

	bool GestureEventQueue::ShouldForwardForBounceReduction(
	const GestureEventWithLatencyInfo& gesture_event) {
	if (debounce_interval_ <= base::TimeDelta())
	return true;

	// Don't debounce any gesture events while a fling is in progress on the
	// browser side. A GSE event in this case ends fling progress and it shouldn't
	// get cancelled by its next GSB event.
	if (fling_controller_.fling_in_progress())
	return true;

	switch (gesture_event.event.GetType()) {
	case WebInputEvent::kGestureScrollUpdate:
	if (!scrolling_in_progress_) {
	debounce_deferring_timer_.Start(
	FROM_HERE,
	debounce_interval_,
	this,
	&GestureEventQueue::SendScrollEndingEventsNow);
	} else {
	// Extend the bounce interval.
	debounce_deferring_timer_.Reset();
	}
	scrolling_in_progress_ = true;
	debouncing_deferral_queue_.clear();
	return true;

	case WebInputEvent::kGestureFlingStart:
	// GestureFlingStart shouldn't be debounced because it is a discrete event
	// signalling the end of a scroll
	debounce_deferring_timer_.Stop();
	GestureEventQueue::SendScrollEndingEventsNow();
	return true;

	case WebInputEvent::kGesturePinchBegin:
	case WebInputEvent::kGesturePinchEnd:
	case WebInputEvent::kGesturePinchUpdate:
	// TODO(rjkroege): Debounce pinch (http://crbug.com/147647)
	return true;
	default:
	if (scrolling_in_progress_) {
	debouncing_deferral_queue_.push_back(gesture_event);
	return false;
	}
	return true;
	}
	}

	void GestureEventQueue::QueueAndForwardIfNecessary(
	const GestureEventWithLatencyInfo& gesture_event) {
	if (allow_multiple_inflight_events_) {
	// Event coalescing should be handled in compositor thread event queue.
	if (gesture_event.event.GetType() == WebInputEvent::kGestureFlingCancel)
	fling_in_progress_ = false;
	else if (gesture_event.event.GetType() == WebInputEvent::kGestureFlingStart)
	fling_in_progress_ = true;
	coalesced_gesture_events_.push_back(gesture_event);
	client_->SendGestureEventImmediately(gesture_event);
	return;
	}

	switch (gesture_event.event.GetType()) {
	case WebInputEvent::kGestureFlingCancel:
	fling_in_progress_ = false;
	break;
	case WebInputEvent::kGestureFlingStart:
	fling_in_progress_ = true;
	break;
	case WebInputEvent::kGesturePinchUpdate:
	case WebInputEvent::kGestureScrollUpdate:
	QueueScrollOrPinchAndForwardIfNecessary(gesture_event);
	return;
	case WebInputEvent::kGestureScrollBegin:
	if (OnScrollBegin(gesture_event))
	return;
	break;
	default:
	break;
	}

	coalesced_gesture_events_.push_back(gesture_event);
	if (coalesced_gesture_events_.size() == 1)
	client_->SendGestureEventImmediately(gesture_event);
	}

	bool GestureEventQueue::OnScrollBegin(
	const GestureEventWithLatencyInfo& gesture_event) {
	// If a synthetic scroll begin is encountered, it can cancel out a previous
	// synthetic scroll end. This allows a later gesture scroll update to coalesce
	// with the previous one. crbug.com/607340.
	bool synthetic = gesture_event.event.data.scroll_begin.synthetic;
	bool have_unsent_events =
	EventsInFlightCount() < coalesced_gesture_events_.size();
	if (synthetic && have_unsent_events) {
	GestureEventWithLatencyInfo* last_event = &coalesced_gesture_events_.back();
	if (last_event->event.GetType() == WebInputEvent::kGestureScrollEnd &&
	last_event->event.data.scroll_end.synthetic) {
	coalesced_gesture_events_.pop_back();
	return true;
	}
	}
	return false;
	}

	void GestureEventQueue::ProcessGestureAck(InputEventAckSource ack_source,
	InputEventAckState ack_result,
	WebInputEvent::Type type,
	const ui::LatencyInfo& latency) {
	TRACE_EVENT0("input", "GestureEventQueue::ProcessGestureAck");

	if (coalesced_gesture_events_.empty()) {
	DLOG(ERROR) << "Received unexpected ACK for event type " << type;
	return;
	}

	if (!allow_multiple_inflight_events_) {
	LegacyProcessGestureAck(ack_source, ack_result, type, latency);
	return;
	}

	// ACKs could come back out of order. We want to cache them to restore the
	// original order.
	for (auto& outstanding_event : coalesced_gesture_events_) {
	if (outstanding_event.ack_state() != INPUT_EVENT_ACK_STATE_UNKNOWN)
	continue;
	if (outstanding_event.event.GetType() == type) {
	outstanding_event.latency.AddNewLatencyFrom(latency);
	outstanding_event.set_ack_info(ack_source, ack_result);
	break;
	}
	}

	AckCompletedEvents();
	}

	void GestureEventQueue::AckCompletedEvents() {
	// Don't allow re-entrancy into this method otherwise
	// the ordering of acks won't be preserved.
	if (processing_acks_)
	return;
	base::AutoReset<bool> process_acks(&processing_acks_, true);
	while (!coalesced_gesture_events_.empty()) {
	auto iter = coalesced_gesture_events_.begin();
	if (iter->ack_state() == INPUT_EVENT_ACK_STATE_UNKNOWN)
	break;
	GestureEventWithLatencyInfoAndAckState event = *iter;
	coalesced_gesture_events_.erase(iter);
	AckGestureEventToClient(event, event.ack_source(), event.ack_state());
	}
	}

	void GestureEventQueue::AckGestureEventToClient(
	const GestureEventWithLatencyInfo& event_with_latency,
	InputEventAckSource ack_source,
	InputEventAckState ack_result) {
	DCHECK(allow_multiple_inflight_events_);

	// Ack'ing an event may enqueue additional gesture events. By ack'ing the
	// event before the forwarding of queued events below, such additional events
	// can be coalesced with existing queued events prior to dispatch.
	client_->OnGestureEventAck(event_with_latency, ack_source, ack_result);

	fling_controller_.OnGestureEventAck(event_with_latency, ack_result);
	}

	void GestureEventQueue::LegacyProcessGestureAck(
	InputEventAckSource ack_source,
	InputEventAckState ack_result,
	WebInputEvent::Type type,
	const ui::LatencyInfo& latency) {
	DCHECK(!allow_multiple_inflight_events_);

	// Events are forwarded one-by-one.
	// It's possible that the ack for the second event in an in-flight,
	// coalesced Gesture{Scroll,Pinch}Update pair is received prior to the first
	// event ack.
	size_t event_index = 0;
	if (ignore_next_ack_ && coalesced_gesture_events_.size() > 1 &&
	coalesced_gesture_events_[0].event.GetType() != type &&
	coalesced_gesture_events_[1].event.GetType() == type) {
	event_index = 1;
	}

	GestureEventWithLatencyInfo event_with_latency =
	coalesced_gesture_events_[event_index];
	DCHECK_EQ(event_with_latency.event.GetType(), type);
	event_with_latency.latency.AddNewLatencyFrom(latency);

	// Ack'ing an event may enqueue additional gesture events. By ack'ing the
	// event before the forwarding of queued events below, such additional events
	// can be coalesced with existing queued events prior to dispatch.
	client_->OnGestureEventAck(event_with_latency, ack_source, ack_result);

	fling_controller_.OnGestureEventAck(event_with_latency, ack_result);

	DCHECK_LT(event_index, coalesced_gesture_events_.size());
	coalesced_gesture_events_.erase(coalesced_gesture_events_.begin() +
	event_index);

	if (ignore_next_ack_) {
	ignore_next_ack_ = false;
	return;
	}

	if (coalesced_gesture_events_.empty())
	return;

	const GestureEventWithLatencyInfo& first_gesture_event =
	coalesced_gesture_events_.front();

	// Check for the coupled GesturePinchUpdate before sending either event,
	// handling the case where the first GestureScrollUpdate ack is synchronous.
	GestureEventWithLatencyInfo second_gesture_event;
	if (first_gesture_event.event.GetType() ==
	WebInputEvent::kGestureScrollUpdate &&
	coalesced_gesture_events_.size() > 1 &&
	coalesced_gesture_events_[1].event.GetType() ==
	WebInputEvent::kGesturePinchUpdate) {
	second_gesture_event = coalesced_gesture_events_[1];
	ignore_next_ack_ = true;
	}

	client_->SendGestureEventImmediately(first_gesture_event);
	if (second_gesture_event.event.GetType() != WebInputEvent::kUndefined)
	client_->SendGestureEventImmediately(second_gesture_event);
	}

	TouchpadTapSuppressionController*
	GestureEventQueue::GetTouchpadTapSuppressionController() {
	return fling_controller_.GetTouchpadTapSuppressionController();
	}

	void GestureEventQueue::FlingHasBeenHalted() {
	fling_in_progress_ = false;
	}

	void GestureEventQueue::ForwardGestureEvent(
	const GestureEventWithLatencyInfo& gesture_event) {
	QueueAndForwardIfNecessary(gesture_event);
	}

	void GestureEventQueue::SendScrollEndingEventsNow() {
	scrolling_in_progress_ = false;
	if (debouncing_deferral_queue_.empty())
	return;
	GestureQueue debouncing_deferral_queue;
	debouncing_deferral_queue.swap(debouncing_deferral_queue_);
	for (GestureQueue::const_iterator it = debouncing_deferral_queue.begin();
	it != debouncing_deferral_queue.end(); it++) {
	if (!fling_controller_.FilterGestureEvent(*it)) {
	QueueAndForwardIfNecessary(*it);
	}
	}
	}

	void GestureEventQueue::QueueScrollOrPinchAndForwardIfNecessary(
	const GestureEventWithLatencyInfo& gesture_event) {
	DCHECK_GE(coalesced_gesture_events_.size(), EventsInFlightCount());
	const size_t unsent_events_count =
	coalesced_gesture_events_.size() - EventsInFlightCount();
	if (!unsent_events_count) {
	coalesced_gesture_events_.push_back(gesture_event);
	if (coalesced_gesture_events_.size() == 1) {
	client_->SendGestureEventImmediately(gesture_event);
	} else if (coalesced_gesture_events_.size() == 2) {
	DCHECK(!ignore_next_ack_);
	// If there is an in-flight scroll, the new pinch can be forwarded
	// immediately, avoiding a potential frame delay between the two
	// (similarly for an in-flight pinch with a new scroll).
	const GestureEventWithLatencyInfo& first_event =
	coalesced_gesture_events_.front();
	if (gesture_event.event.GetType() != first_event.event.GetType() &&
	ui::IsCompatibleScrollorPinch(gesture_event.event,
	first_event.event)) {
	ignore_next_ack_ = true;
	client_->SendGestureEventImmediately(gesture_event);
	}
	}
	return;
	}

	GestureEventWithLatencyInfo* last_event = &coalesced_gesture_events_.back();
	if (last_event->CanCoalesceWith(gesture_event)) {
	last_event->CoalesceWith(gesture_event);
	return;
	}

	if (!ui::IsCompatibleScrollorPinch(gesture_event.event, last_event->event)) {
	coalesced_gesture_events_.push_back(gesture_event);
	return;
	}

	// Extract the last event in queue.
	blink::WebGestureEvent last_gesture_event =
	coalesced_gesture_events_.back().event;
	DCHECK_LE(coalesced_gesture_events_.back().latency.trace_id(),
	gesture_event.latency.trace_id());
	ui::LatencyInfo oldest_latency = coalesced_gesture_events_.back().latency;
	oldest_latency.set_coalesced();
	coalesced_gesture_events_.pop_back();

	// Extract the second last event in queue.
	ui::WebScopedInputEvent second_last_gesture_event = nullptr;
	if (unsent_events_count > 1 &&
	ui::IsCompatibleScrollorPinch(gesture_event.event,
	coalesced_gesture_events_.back().event)) {
	second_last_gesture_event =
	ui::WebInputEventTraits::Clone(coalesced_gesture_events_.back().event);
	DCHECK_LE(coalesced_gesture_events_.back().latency.trace_id(),
	oldest_latency.trace_id());
	oldest_latency = coalesced_gesture_events_.back().latency;
	oldest_latency.set_coalesced();
	coalesced_gesture_events_.pop_back();
	}

	std::pair<blink::WebGestureEvent, blink::WebGestureEvent> coalesced_events =
	ui::CoalesceScrollAndPinch(
	second_last_gesture_event
	? &ui::ToWebGestureEvent(*second_last_gesture_event)
	: nullptr,
	last_gesture_event, gesture_event.event);

	GestureEventWithLatencyInfo scroll_event;
	scroll_event.event = coalesced_events.first;
	scroll_event.latency = oldest_latency;

	GestureEventWithLatencyInfo pinch_event;
	pinch_event.event = coalesced_events.second;
	pinch_event.latency = oldest_latency;

	coalesced_gesture_events_.push_back(scroll_event);
	coalesced_gesture_events_.push_back(pinch_event);
	}

	size_t GestureEventQueue::EventsInFlightCount() const {
	if (allow_multiple_inflight_events_) {
	// Currently unused, can be removed if compositor event queue was enabled by
	// default.
	NOTREACHED();
	return coalesced_gesture_events_.size();
	}

	if (coalesced_gesture_events_.empty())
	return 0;

	if (!ignore_next_ack_)
	return 1;

	DCHECK_GT(coalesced_gesture_events_.size(), 1U);
	return 2;
	}

	} // namespace content