[Sync] Add a simple UI to sync-internals to create UserEvents.

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 3fe7ccaf80450cbba9fa102dcf7a6d8a84705ce9..bf4ad41864b2d61704f70a71a365998d9e6cba40 100644
--- a/chrome/browser/ui/webui/sync_internals_message_handler.h
+++ b/chrome/browser/ui/webui/sync_internals_message_handler.h
@@ -68,6 +68,12 @@ class SyncInternalsMessageHandler : public content::WebUIMessageHandler,
   // Handler for getAllNodes message.  Needs a |request_id| argument.
   void HandleGetAllNodes(const base::ListValue* args);
 
+  // Handler for requests to get UserEvents tab visibility.
+  void HandleRequestUserEventsVisibility(const base::ListValue* args);
+
+  // Handler for writeUserEvent message.
+  void HandleWriteUserEvent(const base::ListValue* args);
+
   // syncer::JsEventHandler implementation.
   void HandleJsEvent(const std::string& name,
                      const syncer::JsEventDetails& details) override;
@@ -111,6 +117,11 @@ class SyncInternalsMessageHandler : public content::WebUIMessageHandler,
 
   browser_sync::ProfileSyncService* GetProfileSyncService();
 
+  // Tries to send dispatch event if the ui has initialized, otherwise the
+  // event is dropped.
+  void TryCallDispatch(const base::Value& name_value,
+                       const base::Value& details_value);
+
   base::WeakPtr<syncer::JsController> js_controller_;
 
   // A flag used to prevent double-registration with ProfileSyncService.