[Sync] Notify observers when IsSyncRequested goes from true to false.

components/browser_sync/browser/profile_sync_service.cc

 // 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.
 
 #include "components/browser_sync/browser/profile_sync_service.h"
 
 #include <stddef.h>
 #include <cstddef>
 #include <map>
 #include <utility>
@@ skipping 2341 matching lines @@
     return NULL;
   return signin_->GetOriginal();
 }
 
 void ProfileSyncService::RequestStart() {
   if (!IsSyncAllowed()) {
     // Sync cannot be requested if it's not allowed.
     return;
   }
   DCHECK(sync_client_);
-  sync_prefs_.SetSyncRequested(true);
-  DCHECK(!signin_.get() || signin_->GetOriginal()->IsAuthenticated());
+  if (!IsSyncRequested()) {
+    sync_prefs_.SetSyncRequested(true);
+    NotifyObservers();
+  }
   startup_controller_->TryStart();
 }
 
 void ProfileSyncService::ReconfigureDatatypeManager() {
   // If we haven't initialized yet, don't configure the DTM as it could cause
   // association to start before a Directory has even been created.
   if (backend_initialized_) {
     DCHECK(backend_.get());
     ConfigureDataTypeManager();
   } else if (HasUnrecoverableError()) {
@@ skipping 163 matching lines @@
 }
 
 std::string ProfileSyncService::unrecoverable_error_message() const {
   return unrecoverable_error_message_;
 }
 
 tracked_objects::Location ProfileSyncService::unrecoverable_error_location()
     const {
   return unrecoverable_error_location_;
 }