Enable set passive touch gestures

src/my-app.html

@@ -116,6 +116,10 @@
   </template>
 
   <script>
+    // Gesture events like tap and track generated from touch will not be
+    // preventable, allowing for better scrolling performance.
+    Polymer.setPassiveTouchGestures(true);
+
     class MyApp extends Polymer.Element {
       static get is() { return 'my-app'; }