[Sync] Replace TalkMediator*/MediatorThread* with PushClient

sync/notifier/invalidation_notifier.h

 // Copyright (c) 2012 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.
 //
 // An implementation of SyncNotifier that wraps an invalidation
 // client.  Handles the details of connecting to XMPP and hooking it
 // up to the invalidation client.
 //
 // You probably don't want to use this directly; use
 // NonBlockingInvalidationNotifier.
@@ skipping 92 matching lines @@
   // Our observers (which must live on the same thread).
   ObserverList<SyncNotifierObserver> observers_;
 
   // The client ID to pass to |chrome_invalidation_client_|.
   std::string invalidation_client_id_;
 
   // The state to pass to |chrome_invalidation_client_|.
   std::string invalidation_state_;
 
   // The XMPP connection manager.
+  // TODO(akalin): Use PushClient instead.
   scoped_ptr<notifier::Login> login_;
 
   // The invalidation client.
   ChromeInvalidationClient invalidation_client_;
 
   DISALLOW_COPY_AND_ASSIGN(InvalidationNotifier);
 };
 
 }  // namespace sync_notifier
 
 #endif  // SYNC_NOTIFIER_INVALIDATION_NOTIFIER_H_