Remove histogram Sync.SyncCycleInterval

Bug: 931045
Change-Id: Id0a290c1e889dbe80b99ba2d806f13d3c3e21a39
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1507653
Auto-Submit: Marc Treib <treib@chromium.org>
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#639726}
diff --git a/components/sync/engine_impl/sync_scheduler_impl.cc b/components/sync/engine_impl/sync_scheduler_impl.cc
index 8cc16fa..6741e77 100644
--- a/components/sync/engine_impl/sync_scheduler_impl.cc
+++ b/components/sync/engine_impl/sync_scheduler_impl.cc
@@ -4,15 +4,12 @@
 
 #include "components/sync/engine_impl/sync_scheduler_impl.h"
 
-#include <algorithm>
 #include <cstring>
 #include <utility>
 
 #include "base/bind.h"
-#include "base/bind_helpers.h"
 #include "base/location.h"
 #include "base/logging.h"
-#include "base/metrics/histogram_macros.h"
 #include "base/rand_util.h"
 #include "base/sequenced_task_runner.h"
 #include "base/threading/platform_thread.h"
@@ -20,7 +17,6 @@
 #include "components/sync/base/logging.h"
 #include "components/sync/engine/sync_engine_switches.h"
 #include "components/sync/engine_impl/backoff_delay_provider.h"
-#include "components/sync/protocol/proto_enum_conversions.h"
 #include "components/sync/protocol/sync.pb.h"
 
 using base::TimeDelta;
@@ -682,13 +678,7 @@
   JobPriority priority = next_sync_cycle_job_priority_;
   next_sync_cycle_job_priority_ = NORMAL_PRIORITY;
 
-  TimeTicks now = TimeTicks::Now();
-  if (!last_sync_cycle_start_.is_null()) {
-    UMA_HISTOGRAM_LONG_TIMES("Sync.SyncCycleInterval",
-                             now - last_sync_cycle_start_);
-  }
-  last_sync_cycle_start_ = now;
-  nudge_tracker_.SetSyncCycleStartTime(now);
+  nudge_tracker_.SetSyncCycleStartTime(TimeTicks::Now());
 
   if (mode_ == CONFIGURATION_MODE) {
     if (pending_configure_params_) {
diff --git a/components/sync/engine_impl/sync_scheduler_impl.h b/components/sync/engine_impl/sync_scheduler_impl.h
index 56f6bf0..27d69fb 100644
--- a/components/sync/engine_impl/sync_scheduler_impl.h
+++ b/components/sync/engine_impl/sync_scheduler_impl.h
@@ -262,10 +262,6 @@
 
   SyncCycleContext* cycle_context_;
 
-  // The last time we ran a sync cycle. Null if we haven't ran one since Chrome
-  // startup. Used for metrics.
-  base::TimeTicks last_sync_cycle_start_;
-
   // TryJob might get called for multiple reasons. It should only call
   // DoPollSyncCycleJob after some time since the last attempt.
   // last_poll_reset_ keeps track of when was last attempt.
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 6dbb245..248a32e 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -118469,6 +118469,9 @@
 </histogram>
 
 <histogram name="Sync.SyncCycleInterval" units="ms">
+  <obsolete>
+    Removed 2019-03.
+  </obsolete>
   <owner>treib@chromium.org</owner>
   <summary>
     The interval between successive sync cycles. Recorded whenever a sync cycle