Add a mechanism to let TracingController invoke JavaScript via TracingUI

content/browser/tracing/tracing_ui.h

 // Copyright (c) 2011 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_BROWSER_TRACING_UI_H_
 #define CONTENT_BROWSER_TRACING_UI_H_
 
 #include "content/public/browser/web_ui_controller.h"
 
 namespace content {
 
 // The C++ back-end for the chrome://tracing webui page.
-class TracingUI : public WebUIController {
+class CONTENT_EXPORT TracingUI : public WebUIController {
  public:
   explicit TracingUI(WebUI* web_ui);
+  virtual ~TracingUI();
+  void OnMonitoringStateChanged(bool is_monitoring);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(TracingUI);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_TRACING_UI_H_