Add histograms to track synced pref changes.

chrome/browser/prefs/synced_pref_change_registrar.h

Index: chrome/browser/prefs/synced_pref_change_registrar.h
diff --git a/chrome/browser/prefs/synced_pref_change_registrar.h b/chrome/browser/prefs/synced_pref_change_registrar.h
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+// Copyright (c) 2013 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.
+
+#ifndef CHROME_BROWSER_PREFS_SYNCED_PREF_CHANGE_REGISTRAR_H_
+#define CHROME_BROWSER_PREFS_SYNCED_PREF_CHANGE_REGISTRAR_H_
+
+#include <map>
+#include <string>
+
+#include "base/callback.h"
+#include "chrome/browser/prefs/pref_service_syncable.h"
+#include "chrome/browser/prefs/synced_pref_observer.h"
+
+// Manages the registration of one or more SyncedPrefObservers on a
+// PrefServiceSyncable. This is modeled after base::PrefChangeRegistrar, and
+// it should be used whenever it's necessary to determine whether a pref change
+// has come from sync or from some other mechanism (managed, UI, external, etc.)
+class SyncedPrefChangeRegistrar : public SyncedPrefObserver {
+ public:
+  // Registered callbacks may optionally take a path argument.
+  // The boolean argument indicates whether (true) or not (false)
+  // the change was a result of syncing.
+  typedef base::Callback<void(bool)> ChangeCallback;
+  typedef base::Callback<void(const std::string&, bool)> NamedChangeCallback;
+
+  explicit SyncedPrefChangeRegistrar(PrefServiceSyncable* pref_service);
+  virtual ~SyncedPrefChangeRegistrar();
+
+  // Register an observer callback for sync change events on the pref at
+  // |path|. Only one callback may be registered per pref.
+  void Add(const char* path, const ChangeCallback& callback);
+  void Add(const char* path, const NamedChangeCallback& callback);
+
+  // Remove the registered observer for |path|.
+  void Remove(const char* path);
+
+  // Remove all registered observers.
+  void RemoveAll();
+
+  // Indicates whether or not an observer is already registered for |path|.
+  bool IsObserved(const char* path) const;
+
+ private:
+  // SyncedPrefObserver implementation
+  virtual void OnSyncedPrefChanged(const std::string& path, bool from_sync)
+      OVERRIDE;
+
+  typedef std::map<std::string, NamedChangeCallback> ObserverMap;
+
+  PrefServiceSyncable* pref_service_;
+  ObserverMap observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(SyncedPrefChangeRegistrar);
+};
+
+#endif  // CHROME_BROWSER_PREFS_SYNCED_PREF_CHANGE_REGISTRAR_H_