fix(browser/utils): calling removeEventListener twice with the same args should not cause errors

Closes #283

Closes #284

Author: sjelin

Diff for: lib/browser/utils.ts

@@ -195,7 +195,7 @@ function zoneAwareRemoveEventListener(self: any, args: any[]) {
   // - When `addEventListener` is called on the global context in strict mode, `this` is undefined
   // see https://github.com/angular/zone.js/issues/190
   var target = self || _global;
-  var eventTask = findExistingRegisteredTask(target, handler, eventName, useCapturing, false);
+  var eventTask = findExistingRegisteredTask(target, handler, eventName, useCapturing, true);
   if (eventTask) {
     eventTask.zone.cancelTask(eventTask);
   } else {

Diff for: test/browser/element.spec.ts

@@ -257,6 +257,13 @@ describe('element', function () {
       button.click();
       expect(log).toEqual('');
     });
+
+    it('should be able to deregister the same event twice', function() {
+      var listener = (event) => {};
+      document.body.addEventListener('click', listener, false);
+      document.body.removeEventListener('click', listener, false);
+      document.body.removeEventListener('click', listener, false);
+    });
   });
 
 });