Fix a race condition in preference metric reporting.

chrome/browser/prefs/synced_pref_change_registrar.cc

 // Copyright 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.
 
 #include "chrome/browser/prefs/synced_pref_change_registrar.h"
 
 #include "base/bind.h"
+#include "chrome/browser/prefs/pref_service_syncable.h"
 
 namespace {
 
 void InvokeUnnamedCallback(
     const SyncedPrefChangeRegistrar::ChangeCallback& callback,
     const std::string& path,
     bool from_sync) {
   callback.Run(from_sync);
 }
 
@@ skipping 39 matching lines @@
 
 void SyncedPrefChangeRegistrar::OnSyncedPrefChanged(const std::string& path,
                                                     bool from_sync) {
   if (pref_service_->IsManagedPreference(path.c_str()))
     return;
   ObserverMap::const_iterator iter = observers_.find(path);
   if (iter == observers_.end())
     return;
   iter->second.Run(path, from_sync);
 }