Lazy initialization for ProcessesEventRouter.

chrome/browser/extensions/event_router.h

Index: chrome/browser/extensions/event_router.h
diff --git a/chrome/browser/extensions/event_router.h b/chrome/browser/extensions/event_router.h
index cbfb1b80abaa432e118121b2660ffba3b6f55416..bcd59d44cdbaba698d7318534f4dcfdc9022978f 100644
--- a/chrome/browser/extensions/event_router.h
+++ b/chrome/browser/extensions/event_router.h
@@ -47,6 +47,16 @@ class EventRouter : public content::NotificationObserver,
     USER_GESTURE_NOT_ENABLED = 2,
   };
 
+  // Observers register interest in events with a particular name and are
+  // notified when a listener is added or removed for that |event_name|.
+  class Observer {
+   public:
+    // Called when a listener is added.
+    virtual void OnListenerAdded(const std::string& event_name) {}
+    // Called when a listener is removed.
+    virtual void OnListenerRemoved(const std::string& event_name) {}
+  };
+
   // Sends an event via ipc_sender to the given extension. Can be called on any
   // thread.
   static void DispatchEvent(IPC::Sender* ipc_sender,
@@ -73,6 +83,12 @@ class EventRouter : public content::NotificationObserver,
 
   EventListenerMap& listeners() { return listeners_; }
 
+  // Registers an observer, interested in listeners that receive the event
+  // |event_name|, to be notified when such a listener is added or removed.
+  // There can currently be only one observer for each distinct |event_name|.
+  void RegisterObserver(Observer* observer,
+                        const std::string& event_name);
+
   // Add or remove the extension as having a lazy background page that listens
   // to the event. The difference from the above methods is that these will be
   // remembered even after the process goes away. We use this list to decide
@@ -253,6 +269,9 @@ class EventRouter : public content::NotificationObserver,
 
   EventListenerMap listeners_;
 
+  typedef std::map<std::string, Observer*> ObserverMap;
+  ObserverMap observers_;
+
   // True if we should dispatch the event signalling that Chrome was updated
   // upon loading an extension.
   bool dispatch_chrome_updated_event_;