Only prevent document touch handlers on initial setup

Elements like core-overlay depend on document touch capturing

src/dispatcher.js

@@ -152,11 +152,11 @@
       }
       this.gestures.push(source);
     },
-    register: function(element) {
+    register: function(element, initial) {
       var l = this.eventSourceList.length;
       for (var i = 0, es; (i < l) && (es = this.eventSourceList[i]); i++) {
         // call eventsource register
-        es.register.call(es, element);
+        es.register.call(es, element, initial);
       }
     },
     unregister: function(element) {

src/platform-events.js

@@ -36,6 +36,5 @@
       }
     }
   }
-
-  dispatcher.register(document);
+  dispatcher.register(document, true);
 })(window.PolymerGestures);

src/touch.js

@@ -34,8 +34,8 @@
       'up',
       'move'
     ],
-    register: function(target) {
-      if (target === document) {
+    register: function(target, initial) {
+      if (initial) {
         return;
       }
       dispatcher.listen(target, this.events);