Gallery.app: Add touch handlers for the zoom/scroll feature.

ui/file_manager/gallery/js/image_editor/image_editor.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.
 
 'use strict';
 
 /**
  * ImageEditor is the top level object that holds together and connects
  * everything needed for image editing.
  *
@@ skipping 729 matching lines @@
     this.dragHappened_ = false;
     e.preventDefault();
   }
 };
 
 /**
  * Touch end handler.
  * @param {TouchEvent} e Event.
  */
 ImageEditor.MouseControl.prototype.onTouchEnd = function(e) {
-  if (!this.dragHappened_ && Date.now() - this.touchStartInfo_.time <=
-                             ImageEditor.MouseControl.MAX_TAP_DURATION_) {
+  if (!this.dragHappened_ &&
+      this.touchStartInfo_ &&
+      Date.now() - this.touchStartInfo_.time <=
+          ImageEditor.MouseControl.MAX_TAP_DURATION_) {
     this.buffer_.onClick(this.touchStartInfo_.x, this.touchStartInfo_.y);
     if (this.previousTouchStartInfo_ &&
         Date.now() - this.previousTouchStartInfo_.time <
             ImageEditor.MouseControl.MAX_DOUBLE_TAP_DURATION_) {
       var prevTouchCircle = new Circle(
           this.previousTouchStartInfo_.x,
           this.previousTouchStartInfo_.y,
           ImageEditor.MouseControl.MAX_DISTANCE_FOR_DOUBLE_TAP_);
       if (prevTouchCircle.inside(this.touchStartInfo_.x,
                                  this.touchStartInfo_.y)) {
@@ skipping 432 matching lines @@
 
 /**
  * Hide the prompt.
  */
 ImageEditor.Prompt.prototype.hide = function() {
   if (!this.prompt_) return;
   this.prompt_.setAttribute('state', 'fadeout');
   // Allow some time for the animation to play out.
   this.setTimer(this.reset.bind(this), 500);
 };