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

chrome/common/render_messages_internal.h

Index: chrome/common/render_messages_internal.h
===================================================================
--- chrome/common/render_messages_internal.h	(revision 14939)
+++ chrome/common/render_messages_internal.h	(working copy)
@@ -1296,6 +1296,14 @@
                       std::string /* argument */,
                       int /* callback id */)
 
+  // Notify the browser that this renderer added a listener to an event.
+  IPC_MESSAGE_CONTROL1(ViewHostMsg_ExtensionAddListener,
+                       std::string /* name */)
+
+  // Notify the browser that this renderer removed a listener from an event.
+  IPC_MESSAGE_CONTROL1(ViewHostMsg_ExtensionRemoveListener,
+                       std::string /* name */)
+
 #if defined(OS_MACOSX)
   // On OSX, we cannot allocated shared memory from within the sandbox, so
   // this call exists for the renderer to ask the browser to allocate memory