Fix ipad dragging issue (#233)

* Fix ipad dragging issue

* Limit touch events to map only

src/google_map.js

@@ -186,6 +186,10 @@ export default class GoogleMap extends Component {
     this.mounted_ = true;
     window.addEventListener('resize', this._onWindowResize);
     window.addEventListener('keydown', this._onKeyDownCapture, true);
+
+    // prevent touch devices from moving the entire browser window on drag
+    window.addEventListener('touchmove', this._onTouchMove);
+
     const mapDom = ReactDOM.findDOMNode(this.refs.google_map_dom);
     // gmap can't prevent map drag if mousedown event already occured
     // the only workaround I find is prevent mousedown native browser event
@@ -313,6 +317,7 @@ export default class GoogleMap extends Component {
     window.removeEventListener('keydown', this._onKeyDownCapture);
     mapDom.removeEventListener('mousedown', this._onMapMouseDownNative, true);
     window.removeEventListener('mouseup', this._onChildMouseUp, false);
+    window.removeEventListener('touchmove', this._onTouchMove);
     detectElementResize.addResizeListener(mapDom, that._mapDomResizeCallback);
 
     if (this.overlay_) {
@@ -814,6 +819,15 @@ export default class GoogleMap extends Component {
     }
   }
 
+  _onTouchMove = (event) => {
+    if (this.refs.google_map_dom) {
+      const mapDom = ReactDOM.findDOMNode(this.refs.google_map_dom);
+      if (mapDom.contains(event.target)) {
+        event.preventDefault();
+      }
+    }
+  }
+
   _isCenterDefined = (center) => center && (
     (isPlainObject(center) && isNumber(center.lat) && isNumber(center.lng)) ||
     (center.length === 2 && isNumber(center[0]) && isNumber(center[1]))