[Extensions Bindings] Introduce a supportsLazyListeners property

extensions/browser/event_router.h

Index: extensions/browser/event_router.h
diff --git a/extensions/browser/event_router.h b/extensions/browser/event_router.h
index d63152df5be3ede2283f2a2e06cdfefe50b38da7..5d7347cbac0099d3e4715ea7df16f79feeb15714 100644
--- a/extensions/browser/event_router.h
+++ b/extensions/browser/event_router.h
@@ -234,6 +234,10 @@ class EventRouter : public KeyedService,
     return &lazy_event_dispatch_util_;
   }
 
+  // Returns true if there is a registered lazy listener for the given
+  // |event_name|.
+  bool HasLazyEventListenerForTesting(const std::string& event_name);
+
  private:
   friend class EventRouterFilterTest;
   friend class EventRouterTest;