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

chrome/renderer/extensions/event_bindings.h

Index: chrome/renderer/extensions/event_bindings.h
===================================================================
--- chrome/renderer/extensions/event_bindings.h	(revision 14939)
+++ chrome/renderer/extensions/event_bindings.h	(working copy)
@@ -9,12 +9,17 @@
 
 #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_".