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// Copyright (c) 2012 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 <string>
#include <vector>
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/metrics/field_trial.h"
// This class is used by the browser process to communicate FieldTrial setting
// (field trial name and group) to any previously started renderers.
// This class registers itself as an observer of FieldTrialList. FieldTrialList
// notifies this class by calling it's OnFieldTrialGroupFinalized method when a
// group is selected (finalized) for a FieldTrial and OnFieldTrialGroupFinalized
// method sends the FieldTrial's name and the group to all renderer processes.
// Each renderer process creates the FieldTrial, and by using a 100% probability
// for the FieldTrial, forces the FieldTrial to have the same group string.
class FieldTrialSynchronizer
: public base::RefCountedThreadSafe<FieldTrialSynchronizer>,
public base::FieldTrialList::Observer {
// Construction also sets up the global singleton instance. This instance is
// used to communicate between the UI and other threads, and is destroyed only
// as the main thread (browser_main) terminates, which means all other threads
// have completed, and will not need this instance any further. It adds itself
// as an observer of FieldTrialList so that it gets notified whenever a group
// is finalized in the browser process.
// Notify all renderer processes about the |group_name| that is finalized for
// the given field trail (|field_trial_name|). This is called on UI thread.
void NotifyAllRenderers(const std::string& field_trial_name,
const std::string& group_name);
// FieldTrialList::Observer methods:
// This method is called by the FieldTrialList singleton when a trial's group
// is finalized. This method contacts all renderers (by calling
// NotifyAllRenderers) to create a FieldTrial that carries the randomly
// selected state from the browser process into all the renderer processes.
void OnFieldTrialGroupFinalized(const std::string& name,
const std::string& group_name) override;
friend class base::RefCountedThreadSafe<FieldTrialSynchronizer>;
~FieldTrialSynchronizer() override;