Files.app: Fix closure error which will raised by the updated compiler.

ui/file_manager/gallery/js/mosaic_mode.js

 // Copyright 2014 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.
 
 /**
  * @param {!Element} container Content container.
  * @param {!ErrorBanner} errorBanner Error banner.
  * @param {!cr.ui.ArrayDataModel} dataModel Data model.
  * @param {!cr.ui.ListSelectionModel} selectionModel Selection model.
  * @param {!VolumeManager} volumeManager Volume manager.
@@ skipping 299 matching lines @@
                  Math.max(0, Mosaic.ANIMATED_SCROLL_DURATION - lastPosition));
     scrollOffset += step;
 
     var oldScrollLeft = this.scrollLeft;
     var newScrollLeft = Math.round(scrollOffset);
 
     if (oldScrollLeft !== newScrollLeft)
       this.scrollLeft = newScrollLeft;
 
     if (step === 0 || this.scrollLeft !== newScrollLeft) {
-      this.scrollAnimation_ = null;
+      this.scrollAnimation_ = 0;
       // Release the hovering lock after a safe delay to avoid hovering
       // a tile because of altering |this.scrollLeft|.
       setTimeout(function() {
         if (!this.scrollAnimation_)
           this.suppressHovering_ = false;
       }.bind(this), 100);
     } else {
       // Continue the animation.
       this.scrollAnimation_ = requestAnimationFrame(animationFrame);
     }
@@ skipping 1978 matching lines @@
   return new ImageRect(this.left_ - this.container_.scrollLeft, this.top_,
       this.width_, this.height_).inflate(-margin, -margin);
 };
 
 /**
  * @return {number} X coordinate of the tile center.
  */
 Mosaic.Tile.prototype.getCenterX = function() {
   return this.left_ + Math.round(this.width_ / 2);
 };