Add a mechanism to let TracingController invoke JavaScript via TracingUI

content/browser/tracing/tracing_ui.h

Index: content/browser/tracing/tracing_ui.h
diff --git a/content/browser/tracing/tracing_ui.h b/content/browser/tracing/tracing_ui.h
index 85bbce15c2cb427387258e532da46b7b8d65fd83..40ce0821e2d49a05711cadc43c8ea8900a0e37b5 100644
--- a/content/browser/tracing/tracing_ui.h
+++ b/content/browser/tracing/tracing_ui.h
@@ -10,9 +10,11 @@
 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);