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

chrome/renderer/extensions/event_bindings.cc

Index: chrome/renderer/extensions/event_bindings.cc
===================================================================
--- chrome/renderer/extensions/event_bindings.cc	(revision 14939)
+++ chrome/renderer/extensions/event_bindings.cc	(working copy)
@@ -6,6 +6,7 @@
 
 #include "base/basictypes.h"
 #include "base/singleton.h"
+#include "chrome/common/render_messages.h"
 #include "chrome/renderer/extensions/bindings_utils.h"
 #include "chrome/renderer/extensions/event_bindings.h"
 #include "chrome/renderer/js_only_v8_extensions.h"
@@ -14,16 +15,33 @@
 
 namespace {
 
+// Keep a local cache of RenderThread so that we can mock it out for unit tests.
+static RenderThreadBase* render_thread = NULL;
+
+static RenderThreadBase* GetRenderThread() {
+  return render_thread ? render_thread : RenderThread::current();
+}
+
 // Keep a list of contexts that have registered themselves with us.  This lets
 // us know where to dispatch events when we receive them.
 typedef std::list< v8::Persistent<v8::Context> > ContextList;
 struct ExtensionData {
   ContextList contexts;
+  std::map<std::string, int> listener_count;
 };
 ContextList& GetRegisteredContexts() {
   return Singleton<ExtensionData>::get()->contexts;
 }
+int EventIncrementListenerCount(const std::string& event_name) {
+  ExtensionData *data = Singleton<ExtensionData>::get();
+  return ++(data->listener_count[event_name]);
+}
+int EventDecrementListenerCount(const std::string& event_name) {
+  ExtensionData *data = Singleton<ExtensionData>::get();
+  return --(data->listener_count[event_name]);
+}
 
+
 const char* kExtensionDeps[] = { JsonJsV8Extension::kName };
 const char* kContextAttachCount = "chromium.attachCount";
 
@@ -47,10 +65,11 @@
   }
 
   // Attach an event name to an object.
-  // TODO(mpcomplete): I'm just using this to register the v8 Context right now.
-  // The idea is to eventually notify the browser about what events are being
-  // listened to, so it can dispatch appropriately.
   static v8::Handle<v8::Value> AttachEvent(const v8::Arguments& args) {
+    DCHECK(args.Length() == 1);
+    // TODO(erikkay) should enforce that event name is a string in the bindings
+    DCHECK(args[0]->IsString() || args[0]->IsUndefined());
+
     v8::Persistent<v8::Context> context =
         v8::Persistent<v8::Context>::New(v8::Context::GetCurrent());
     v8::Local<v8::Object> global = context->Global();
@@ -71,10 +90,22 @@
         v8::String::New(kContextAttachCount),
         v8::Integer::New(account_count_value + 1));
 
+    if (args[0]->IsString()) {
+      std::string event_name(*v8::String::AsciiValue(args[0]));
+      if (EventIncrementListenerCount(event_name) == 1) {
+        GetRenderThread()->Send(
+            new ViewHostMsg_ExtensionAddListener(event_name));
+      }
+    }
+
     return v8::Undefined();
   }
 
   static v8::Handle<v8::Value> DetachEvent(const v8::Arguments& args) {
+    DCHECK(args.Length() == 1);
+    // TODO(erikkay) should enforce that event name is a string in the bindings
+    DCHECK(args[0]->IsString() || args[0]->IsUndefined());
+
     v8::Local<v8::Context> context = v8::Context::GetCurrent();
     v8::Local<v8::Object> global = context->Global();
     v8::Local<v8::Value> attach_count = global->GetHiddenValue(
@@ -90,6 +121,14 @@
         v8::String::New(kContextAttachCount),
         v8::Integer::New(account_count_value - 1));
 
+    if (args[0]->IsString()) {
+      std::string event_name(*v8::String::AsciiValue(args[0]));
+      if (EventDecrementListenerCount(event_name) == 0) {
+        GetRenderThread()->Send(
+          new ViewHostMsg_ExtensionRemoveListener(event_name));
+      }
+    }
+
     return v8::Undefined();
   }
 
@@ -122,6 +161,11 @@
   return new ExtensionImpl();
 }
 
+// static
+void EventBindings::SetRenderThread(RenderThreadBase* thread) {
+  render_thread = thread;
+}
+
 void EventBindings::CallFunction(const std::string& function_name,
                                  int argc, v8::Handle<v8::Value>* argv) {
   for (ContextList::iterator it = GetRegisteredContexts().begin();