fix($rootScope): avoid unstable reference in $broadcast event

The event.currentScope was a reference to the iterator of the scope traversal (`current`). It caused problems when accessing the event.currentScope asynchronously : it was the last scope of the traversal instead of the scope which listen the event.

Author: ncuillery

src/ng/rootScope.js

@@ -1096,23 +1096,25 @@ function $RootScopeProvider(){
        * @return {Object} Event object, see {@link ng.$rootScope.Scope#$on}
        */
       $broadcast: function(name, args) {
+        function Event(currentScope) {
+          this.name = name;
+          this.currentScope = currentScope;
+          this.targetScope = target;
+          this.defaultPrevented = false;
+        }
+        Event.prototype.preventDefault = function() {
+          this.defaultPrevented = true;
+        }
+
         var target = this,
             current = target,
             next = target,
-            event = {
-              name: name,
-              targetScope: target,
-              preventDefault: function() {
-                event.defaultPrevented = true;
-              },
-              defaultPrevented: false
-            },
-            listenerArgs = concat([event], arguments, 1),
+            listenerArgs,
+            event = new Event(current),
             listeners, i, length;
 
         //down while you can, then up and next sibling or up and next sibling until back at root
         while ((current = next)) {
-          event.currentScope = current;
           listeners = current.$$listeners[name] || [];
           for (i=0, length = listeners.length; i<length; i++) {
             // if listeners were deregistered, defragment the array
@@ -1124,6 +1126,8 @@ function $RootScopeProvider(){
             }
 
             try {
+              event = new Event(current);
+              listenerArgs = concat([event], arguments, 1);
               listeners[i].apply(null, listenerArgs);
             } catch(e) {
               $exceptionHandler(e);

test/ng/rootScopeSpec.js

@@ -1700,6 +1700,7 @@ describe('Scope', function() {
         it('should receive event object', inject(function($rootScope) {
           var scope = $rootScope,
               child = scope.$new(),
+              grandChild = child.$new(),
               event;
 
           child.$on('fooEvent', function(e) {