Move sync notifier contruction out of syncer thread.

chrome/browser/sync/notifier/sync_notifier.h

 // Copyright (c) 2011 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.
 //
 // Interface to the sync notifier, which is an object that receives
 // notifications when updates are available for a set of sync types.
 // All the observers are notified when such an event happens.
+//
+// A SyncNotifier must be destroyed on the same thread it was created on,
+// and all its methods must be called on the same thread (not necessarily
+// the one it was created on). If the methods thread is different from the
+// creation thread, then the methods thread must not exist when the SyncNotifier
+// is created and destroyed.
+//
+// In particular, the SyncNotifier will be created on the UI thread, the syncer
+// core thread will be created, the SyncNotifier will be used on that core
+// thread, the syncer core thread will be destroyed, and then the SyncNotifier
+// will be destroyed.
+//
+// TODO(akalin): Remove the code to deal with this situation once the syncer
+// core thread goes away.
 
 #ifndef CHROME_BROWSER_SYNC_NOTIFIER_SYNC_NOTIFIER_H_
 #define CHROME_BROWSER_SYNC_NOTIFIER_SYNC_NOTIFIER_H_
 
 #include <string>
 
 #include "chrome/browser/sync/syncable/model_type.h"
 
 namespace sync_notifier {
 class SyncNotifierObserver;
@@ skipping 20 matching lines @@
   // This is here only to support the old p2p notification implementation,
   // which is still used by sync integration tests.
   // TODO(akalin): Remove this once we move the integration tests off p2p
   // notifications.
   virtual void SendNotification() = 0;
 };
 }  // namespace sync_notifier
 
 #endif  // CHROME_BROWSER_SYNC_NOTIFIER_SYNC_NOTIFIER_H_