[Sync] Avoid ObserverListThreadSafe in ChromeSyncNotificationBridge

chrome/browser/sync/glue/chrome_sync_notification_bridge.cc

Index: chrome/browser/sync/glue/chrome_sync_notification_bridge.cc
diff --git a/chrome/browser/sync/glue/chrome_sync_notification_bridge.cc b/chrome/browser/sync/glue/chrome_sync_notification_bridge.cc
index 9936fa08f020e93b0eff6fe86a1dcbecc3f81db8..78212d21b3f69bce073b10f088aaf66194effaaa 100644
--- a/chrome/browser/sync/glue/chrome_sync_notification_bridge.cc
+++ b/chrome/browser/sync/glue/chrome_sync_notification_bridge.cc
@@ -4,6 +4,9 @@
 
 #include "chrome/browser/sync/glue/chrome_sync_notification_bridge.h"
 
+#include "base/bind.h"
+#include "base/location.h"
+#include "base/observer_list.h"
 #include "chrome/common/chrome_notification_types.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/notification_service.h"
@@ -13,10 +16,73 @@ using content::BrowserThread;
 
 namespace browser_sync {
 
+class ChromeSyncNotificationBridge::Core
+    : public base::RefCountedThreadSafe<Core> {
+ public:
+  // Created on UI thread.
+  explicit Core(
+      const scoped_refptr<base::SequencedTaskRunner>& sync_task_runner);
+
+  // All member functions below must be called on the sync task runner.
+
+  void AddObserver(syncer::SyncNotifierObserver* observer);
+  void RemoveObserver(syncer::SyncNotifierObserver* observer);
+
+  void EmitNotification(
+      syncer::ModelTypePayloadMap payload_map,
+      syncer::IncomingNotificationSource notification_source);
+
+ private:
+  friend class base::RefCountedThreadSafe<Core>;
+
+  // Destroyed on the UI thread or on |sync_task_runner_|.
+  ~Core();
+
+  const scoped_refptr<base::SequencedTaskRunner> sync_task_runner_;
+
+  // Used only on |sync_task_runner_|.
+  syncer::ModelTypeSet enabled_types_;
+  ObserverList<syncer::SyncNotifierObserver> observers_;
+};
+
+ChromeSyncNotificationBridge::Core::Core(
+    const scoped_refptr<base::SequencedTaskRunner>& sync_task_runner)
+    : sync_task_runner_(sync_task_runner) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  DCHECK(sync_task_runner_.get());
+}
+
+ChromeSyncNotificationBridge::Core::~Core() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI) ||
+         sync_task_runner_->RunsTasksOnCurrentThread());
+}
+
+void ChromeSyncNotificationBridge::Core::AddObserver(
+    syncer::SyncNotifierObserver* observer) {
+  DCHECK(sync_task_runner_->RunsTasksOnCurrentThread());
+  observers_.AddObserver(observer);
+}
+
+void ChromeSyncNotificationBridge::Core::RemoveObserver(
+    syncer::SyncNotifierObserver* observer) {
+  DCHECK(sync_task_runner_->RunsTasksOnCurrentThread());
+  observers_.RemoveObserver(observer);
+}
+
+void ChromeSyncNotificationBridge::Core::EmitNotification(
+    syncer::ModelTypePayloadMap payload_map,
+    syncer::IncomingNotificationSource notification_source) {
+  DCHECK(sync_task_runner_->RunsTasksOnCurrentThread());
+  FOR_EACH_OBSERVER(
+      syncer::SyncNotifierObserver, observers_,
+      OnIncomingNotification(payload_map, notification_source));
+}
+
 ChromeSyncNotificationBridge::ChromeSyncNotificationBridge(
-    const Profile* profile)
-    : observers_(
-        new ObserverListThreadSafe<syncer::SyncNotifierObserver>()) {
+    const Profile* profile,
+    const scoped_refptr<base::SequencedTaskRunner>& sync_task_runner)
+    : sync_task_runner_(sync_task_runner),
+      core_(new Core(sync_task_runner_)) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   DCHECK(profile);
   registrar_.Add(this, chrome::NOTIFICATION_SYNC_REFRESH_LOCAL,
@@ -35,12 +101,14 @@ void ChromeSyncNotificationBridge::UpdateEnabledTypes(
 
 void ChromeSyncNotificationBridge::AddObserver(
     syncer::SyncNotifierObserver* observer) {
-  observers_->AddObserver(observer);
+  DCHECK(sync_task_runner_->RunsTasksOnCurrentThread());
+  core_->AddObserver(observer);
 }
 
 void ChromeSyncNotificationBridge::RemoveObserver(
     syncer::SyncNotifierObserver* observer) {
-  observers_->RemoveObserver(observer);
+  DCHECK(sync_task_runner_->RunsTasksOnCurrentThread());
+  core_->RemoveObserver(observer);
 }
 
 void ChromeSyncNotificationBridge::Observe(
@@ -55,7 +123,7 @@ void ChromeSyncNotificationBridge::Observe(
   } else if (type == chrome::NOTIFICATION_SYNC_REFRESH_REMOTE) {
     notification_source = syncer::REMOTE_NOTIFICATION;
   } else {
-    NOTREACHED() << "Unexpected notification type:" << type;
+    NOTREACHED() << "Unexpected notification type: " << type;
     return;
   }
 
@@ -69,9 +137,10 @@ void ChromeSyncNotificationBridge::Observe(
         syncer::ModelTypePayloadMapFromEnumSet(enabled_types_, std::string());
   }
 
-  observers_->Notify(
-      &syncer::SyncNotifierObserver::OnIncomingNotification,
-      payload_map, notification_source);
+  sync_task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&Core::EmitNotification,
+                 core_, payload_map, notification_source));
 }
 
 }  // namespace browser_sync