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// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef CONTENT_BROWSER_FIELD_TRIAL_SYNCHRONIZER_H_
#define CONTENT_BROWSER_FIELD_TRIAL_SYNCHRONIZER_H_
#include <string>
#include <vector>
#include "base/metrics/field_trial.h"
#include "components/variations/variations_ids_provider.h"
namespace content {
class RenderProcessHost;
// This class is used by the browser process to communicate FieldTrial setting
// (field trial name and group) and Variation header to any previously started
// renderers.
//
// This class registers itself as an observer of FieldTrialList. FieldTrialList
// notifies this class by calling its 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. This
// is mostly an optimization so that renderers don't send anything to the
// browser when they know that a trial is already active.
//
// This class also registers itself as a VariationsIdsProvider Observer and
// updates the renderers if the variations header changes.
class FieldTrialSynchronizer
: public base::FieldTrialList::Observer,
public variations::VariationsIdsProvider::Observer {
public:
// Creates the global FieldTrialSynchronizer instance for this process. After
// this is invoked, renderers are notified whenever a field trial group is
// finalized.
static void CreateInstance();
FieldTrialSynchronizer(const FieldTrialSynchronizer&) = delete;
FieldTrialSynchronizer& operator=(const FieldTrialSynchronizer&) = delete;
// 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 base::FieldTrial& trial,
const std::string& group_name) override;
// VariationsIdsProvider::Observer methods:
void VariationIdsHeaderUpdated() override;
// Sends the current variations header to |host|'s renderer.
static void UpdateRendererVariationsHeader(RenderProcessHost* host);
private:
FieldTrialSynchronizer();
~FieldTrialSynchronizer() override;
static void NotifyAllRenderersOfVariationsHeader();
};
} // namespace content
#endif // CONTENT_BROWSER_FIELD_TRIAL_SYNCHRONIZER_H_
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