Make sure we only actually call _listen once

Gestures have counter code that should not be re-added with multiple identical
`listen` calls

src/standard/events.html

@@ -85,7 +85,12 @@
       if (!handler) {
         handler = this._createEventHandler(node, eventName, methodName);
       }
+      // don't call _listen if we are already listening
+      if (handler._listening) {
+        return;
+      }
       this._listen(node, eventName, handler);
+      handler._listening = true;
     },
 
     _boundListenerKey: function(eventName, methodName) {
@@ -129,6 +134,7 @@
             methodName + '` not defined'));
         }
       };
+      handler._listening = false;
       this._recordEventHandler(host, eventName, node, methodName, handler);
       return handler;
     },
@@ -148,6 +154,7 @@
       var handler = this._recallEventHandler(this, eventName, node, methodName);
       if (handler) {
         this._unlisten(node, eventName, handler);
+        handler._listening = false;
       }
     },
 

test/unit/events.html

@@ -153,6 +153,11 @@
           document.body.removeChild(el);
         });
 
+        test('listen marks event handler as listening', function() {
+          var handler = el._recallEventHandler(el, 'foo', el, 'missing');
+          assert.equal(handler._listening, true, 'handler should be marked');
+        });
+
         test('Event handler fires only once', function() {
           el.fire('foo');
           assert.equal(el._warned.length, 1, 'event should fire only once');
@@ -171,9 +176,14 @@
           assert.ok(fn, 'should be cached');
         });
 
+        test('unlisten markes cached handler as not listening', function() {
+          var handler = el._recallEventHandler(el, 'foo', el, 'missing');
+          assert.equal(handler._listening, false, 'handler should not be listening');
+        });
+
         test('once unlistened, no handler fire', function() {
           el.fire('foo');
-          assert.equal(el._warned.length, 1, 'event should not be handled anymore')
+          assert.equal(el._warned.length, 1, 'event should not be handled anymore');
         });
       });
     });