about:sync: Fix refresh crash and broken node browser

chrome/browser/ui/webui/sync_internals_message_handler.h

Index: chrome/browser/ui/webui/sync_internals_message_handler.h
diff --git a/chrome/browser/ui/webui/sync_internals_message_handler.h b/chrome/browser/ui/webui/sync_internals_message_handler.h
index 971374aed9c6a7dee91e0f1c36d6bfb46017f2f9..833a4fcebc430760b55b8dd610b23a7711879d9f 100644
--- a/chrome/browser/ui/webui/sync_internals_message_handler.h
+++ b/chrome/browser/ui/webui/sync_internals_message_handler.h
@@ -66,6 +66,10 @@ class SyncInternalsMessageHandler
   ProfileSyncService* GetProfileSyncService();
 
   base::WeakPtr<syncer::JsController> js_controller_;
+
+  // A flag used to prevent double-registration with ProfileSyncService.
+  bool is_registered_;
+
   base::WeakPtrFactory<SyncInternalsMessageHandler> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncInternalsMessageHandler);