WebUI: Add helper FireWebUIListener method on WebUIMessageHandler.

content/public/browser/web_ui_message_handler.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.
 
 #ifndef CONTENT_PUBLIC_BROWSER_WEB_UI_MESSAGE_HANDLER_H_
 #define CONTENT_PUBLIC_BROWSER_WEB_UI_MESSAGE_HANDLER_H_
 
 #include <vector>
 
 #include "base/gtest_prod_util.h"
 #include "base/logging.h"
 #include "base/strings/string16.h"
+#include "base/values.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/web_ui.h"
 
 class WebUIBrowserTest;
 
 namespace base {
 class ListValue;
-class Value;
 }
 
 namespace content {
 
 class WebUI;
 class WebUIImpl;
 
 // Messages sent from the DOM are forwarded via the WebUI to handler
 // classes. These objects are owned by WebUI and destroyed when the
 // host is destroyed.
@@ skipping 53 matching lines @@
   // promise should be resolved (request succeeded).
   void ResolveJavascriptCallback(const base::Value& callback_id,
                                  const base::Value& response);
 
   // Helper method for responding to Javascript requests initiated with
   // cr.sendWithPromise() (defined in cr.js), for the case where the returned
   // promise should be rejected (request failed).
   void RejectJavascriptCallback(const base::Value& callback_id,
                                 const base::Value& response);
 
+  // Helper method for notifying Javascript listeners added with
+  // cr.addWebUIListener() (defined in cr.js).
+  template <typename... Values>
+  void FireWebUIListener(const std::string& event_name,
+                         const Values&... values) {
+    // cr.webUIListenerCallback is a global JS function exposed from cr.js.
+    CallJavascriptFunction("cr.webUIListenerCallback", base::Value(event_name),
+                           values...);
+  }
+
   // Call a Javascript function by sending its name and arguments down to
   // the renderer.  This is asynchronous; there's no way to get the result
   // of the call, and should be thought of more like sending a message to
   // the page.
   // All function names in WebUI must consist of only ASCII characters.
   // These functions will crash if JavaScript is not currently allowed.
   template <typename... Values>
   void CallJavascriptFunction(const std::string& function_name,
                               const Values&... values) {
     CHECK(IsJavascriptAllowed()) << "Cannot CallJavascriptFunction before "
@@ skipping 20 matching lines @@
 
   // True if the page is for JavaScript calls from this handler.
   bool javascript_allowed_;
 
   WebUI* web_ui_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_WEB_UI_MESSAGE_HANDLER_H_