[Sync] Avoid ObserverListThreadSafe in ChromeSyncNotificationBridge

chrome/browser/sync/glue/sync_backend_host.h

Index: chrome/browser/sync/glue/sync_backend_host.h
diff --git a/chrome/browser/sync/glue/sync_backend_host.h b/chrome/browser/sync/glue/sync_backend_host.h
index 5bfb0cfa6820b985e25d819c911bc08a88a17f6e..f49e05d4f20da99bb12d063501559d94fb1619be 100644
--- a/chrome/browser/sync/glue/sync_backend_host.h
+++ b/chrome/browser/sync/glue/sync_backend_host.h
@@ -16,7 +16,6 @@
 #include "base/threading/thread.h"
 #include "chrome/browser/sync/glue/backend_data_type_configurer.h"
 #include "chrome/browser/sync/glue/chrome_extensions_activity_monitor.h"
-#include "chrome/browser/sync/glue/chrome_sync_notification_bridge.h"
 #include "chrome/common/net/gaia/google_service_auth_error.h"
 #include "googleurl/src/gurl.h"
 #include "sync/internal_api/public/base/model_type.h"
@@ -41,6 +40,7 @@ class SyncManagerFactory;
 namespace browser_sync {
 
 class ChangeProcessor;
+class ChromeSyncNotificationBridge;
 struct Experiments;
 class InvalidatorStorage;
 class JsBackend;
@@ -477,9 +477,9 @@ class SyncBackendHost : public BackendDataTypeConfigurer {
 
   const base::WeakPtr<SyncPrefs> sync_prefs_;
 
-  // A thread-safe listener for handling notifications triggered by
-  // chrome events.
-  ChromeSyncNotificationBridge chrome_sync_notification_bridge_;
+  // A bridge that converts Chrome notifications (on the UI thread)
+  // into invalidations (on the sync thread).
+  scoped_ptr<ChromeSyncNotificationBridge> chrome_sync_notification_bridge_;
 
   syncer::SyncNotifierFactory sync_notifier_factory_;