perf(Scope): exit $broadcast early if nobody is listening for the given event

src/ng/rootScope.js

@@ -1148,8 +1148,11 @@ function $RootScopeProvider(){
                 event.defaultPrevented = true;
               },
               defaultPrevented: false
-            },
-            listenerArgs = concat([event], arguments, 1),
+            };
+
+        if (!target.$$listenerCount[name]) return event;
+
+        var listenerArgs = concat([event], arguments, 1),
             listeners, i, length;
 
         //down while you can, then up and next sibling or up and next sibling until back at root