Normalizing .dropEffect across platforms (specifically Windows).

chrome/browser/resources/ntp4/tile_page.js

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 cr.define('ntp4', function() {
   'use strict';
 
   // We can't pass the currently dragging tile via dataTransfer because of
   // http://crbug.com/31037
   var currentlyDraggingTile = null;
@@ skipping 133 matching lines @@
      * @param {Event} e The event for the drag.
      * @private
      */
     onDragEnd_: function(e) {
       this.dragClone.hidden = false;
       this.dragClone.classList.add('placing');
 
       setCurrentlyDraggingTile(null);
 
       // tilePage will be null if we've already been removed.
-      if (this.tilePage)
-        this.tilePage.positionTile_(this.index);
+      var tilePage = this.tilePage;
+      if (tilePage)
+        tilePage.positionTile_(this.index);
 
       // Take an appropriate action with the drag clone.
       if (this.landedOnTrash) {
         this.dragClone.classList.add('deleting');
-      } else if (this.tilePage) {
-        if (this.tilePage.selected && e.dataTransfer.dropEffect != 'copy') {
+      } else if (tilePage) {
+        // TODO(dbeam): Until we fix dropEffect to the correct behavior it will
+        // differ on windows - crbug.com/39399.  That's why we use the custom
+        // tilePage.lastDropEffect_ instead of e.dataTransfer.dropEffect.
+        if (tilePage.selected && tilePage.lastDropEffect_ != 'copy') {
           // The drag clone can still be hidden from the last drag move event.
           this.dragClone.hidden = false;
           // The tile's contents may have moved following the respositioning;
           // adjust for that.
           var contentDiffX = this.dragClone.firstChild.offsetLeft -
               this.firstChild.offsetLeft;
           var contentDiffY = this.dragClone.firstChild.offsetTop -
               this.firstChild.offsetTop;
           this.dragClone.style.left = (this.gridX + this.parentNode.offsetLeft -
               contentDiffX) + 'px';
@@ skipping 748 matching lines @@
      * @param {Event} e A mouseover event for the drag over.
      */
     doDragOver: function(e) {
       e.preventDefault();
 
       this.setDropEffect(e.dataTransfer);
       var newDragIndex = this.getWouldBeIndexForPoint_(e.pageX, e.pageY);
       if (newDragIndex < 0 || newDragIndex >= this.tileElements_.length)
         newDragIndex = this.dragItemIndex_;
       this.updateDropIndicator_(newDragIndex);
+
+      this.lastDropEffect_ = e.dataTransfer.dropEffect;
     },
 
     /**
      * Performs all actions necessary when the user completes a drop.
      * @param {Event} e A mouseover event for the drag drop.
      */
     doDrop: function(e) {
       e.stopPropagation();
 
       var index = this.currentDropIndex_;
@@ skipping 121 matching lines @@
     setDropEffect: function(dataTransfer) {
       assert(false);
     },
   };
 
   return {
     getCurrentlyDraggingTile: getCurrentlyDraggingTile,
     TilePage: TilePage,
   };
 });