Only send events to renderers that are listening to an event....

chrome/renderer/extensions/event_bindings.h

 // Copyright (c) 2009 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 CHROME_RENDERER_EXTENSIONS_EVENT_BINDINGS_H_
 #define CHROME_RENDERER_EXTENSIONS_EVENT_BINDINGS_H_
 
 #include "v8/include/v8.h"
 
 #include <string>
 
+class RenderThreadBase;
+
 // This class deals with the javascript bindings related to Event objects.
 class EventBindings {
  public:
   static const char* kName;  // The v8::Extension name, for dependencies.
   static v8::Extension* Get();
 
+  // Allow RenderThread to be mocked out.
+  static void SetRenderThread(RenderThreadBase* thread);
+
   // Calls the given function in each registered context which is listening
   // for events.  The function can be an object property, ie:
   // "chromium.Event.dispatch_".
   static void CallFunction(const std::string& function_name, int argc,
                            v8::Handle<v8::Value>* argv);
 };
 
 #endif  // CHROME_RENDERER_EXTENSIONS_EVENT_BINDINGS_H_