DevTools: Allow several drag handlers running simultaneously.

third_party/WebKit/Source/devtools/front_end/ui_lazy/OverviewGrid.js

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 260 matching lines @@
 
     /**
      * @param {!Event} event
      * @return {boolean}
      */
     _startWindowDragging: function(event)
     {
         this._dragStartPoint = event.pageX;
         this._dragStartLeft = this.windowLeft;
         this._dragStartRight = this.windowRight;
+        event.stopPropagation();
         return true;
     },
 
     /**
      * @param {!Event} event
      */
     _windowDragging: function(event)
     {
         event.preventDefault();
         var delta = (event.pageX - this._dragStartPoint) / this._parentElement.clientWidth;
@@ skipping 165 matching lines @@
         position = Math.max(0, Math.min(position, this._width));
         if (position < this._startPosition) {
             this._windowSelector.style.left = position + "px";
             this._windowSelector.style.right = this._width - this._startPosition + "px";
         } else {
             this._windowSelector.style.left = this._startPosition + "px";
             this._windowSelector.style.right = this._width - position + "px";
         }
     }
 };