Don't load all bytes of video when generating thumbnails.

ui/file_manager/image_loader/request.js

 // Copyright 2013 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.
 
 /**
  * @typedef {{
  *   cache: (boolean|undefined),
  *   priority: (number|undefined),
  *   taskId: number,
  *   timestamp: (number|undefined),
@@ skipping 228 matching lines @@
   }.bind(this);
 
   // Download data urls directly since they are not supported by XmlHttpRequest.
   var dataUrlMatches = this.request_.url.match(/^data:([^,;]*)[,;]/);
   if (dataUrlMatches) {
     this.image_.src = this.request_.url;
     this.contentType_ = dataUrlMatches[1];
     return;
   }
 
+  var fileType = FileType.getTypeForName(this.request_.url);
+
   // Load RAW images by using Piex loader instead of XHR.
-  var fileType = FileType.getTypeForName(this.request_.url);
   if (fileType.type === 'raw') {
     var timer = metrics.getTracker().startTiming(
         metrics.Categories.INTERNALS,
         metrics.timing.Variables.EXTRACT_THUMBNAIL_FROM_RAW,
         fileType.subtype);
     this.piexLoader_.load(this.request_.url).then(function(data) {
       timer.send();
       var blob = new Blob([data.thumbnail], {type: 'image/jpeg'});
       var url = URL.createObjectURL(blob);
       this.image_.src = url;
       this.request_.orientation = data.orientation;
       this.request_.colorSpace = data.colorSpace;
     }.bind(this), function(error) {
       console.error('PiexLoaderError: ', error);
       onFailure();
     });
     return;
   }
 
+  // Load video thumbnails by using video tag instead of XHR.
+  if (fileType.type === 'video') {
+    this.createVideoThumbnailUrl_(this.request_.url).then(function(url) {
+      this.image_.src = url;
+    }.bind(this)).catch(function(error) {
+      console.error('Video thumbnail error: ', error);
+      onFailure();
+    });
+    return;
+  }
+
   // Fetch the image via authorized XHR and parse it.
   var parseImage = function(contentType, blob) {
     if (contentType)
       this.contentType_ = contentType;
-    if (fileType.type === 'video') {
-      this.createThumbnailUrl_(blob).then(function(url) {
-        this.image_.src = url;
-      }.bind(this), onFailure);
-    } else {
-      this.image_.src = URL.createObjectURL(blob);
-    }
+    this.image_.src = URL.createObjectURL(blob);
   }.bind(this);
 
   // Request raw data via XHR.
   this.xhr_.load(this.request_.url, parseImage, onFailure);
 };
 
 /**
  * Creates a video thumbnail data url from video file.
  *
- * @param {!Blob}  blob Blob object of video file
- * @return {!Promise<!string>}  Promise that resolves with the data url of video
+ * @param {string} url Video URL.
+ * @return {!Promise<Blob>}  Promise that resolves with the data url of video
  *    thumbnail.
  * @private
  */
-ImageRequest.prototype.createThumbnailUrl_ = function(blob) {
-  var url = URL.createObjectURL(blob);
+ImageRequest.prototype.createVideoThumbnailUrl_ = function(url) {
   var video = document.createElement('video');
   return new Promise(function(resolve, reject) {
     video.addEventListener('canplay', resolve);
     video.addEventListener('error', reject);
     video.currentTime = ImageRequest.VIDEO_THUMBNAIL_POSITION;
     video.preload = 'auto';
     video.src = url;
   }).then(function() {
-    URL.revokeObjectURL(url);
     var canvas = document.createElement('canvas');
     canvas.width = video.videoWidth;
     canvas.height = video.videoHeight;
     canvas.getContext('2d').drawImage(video, 0, 0);
     return canvas.toDataURL();
-  }, function(errev) {
-    URL.revokeObjectURL(url);
-    console.error(errev);
-    return Promise.reject(errev);
   });
 };
 
 /**
  * Creates a XmlHttpRequest wrapper with injected OAuth2 authentication headers.
  * @constructor
  */
 function AuthorizedXHR() {
   this.xhr_ = null;
   this.aborted_ = false;
@@ skipping 257 matching lines @@
   this.image_.src = 'data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAA' +
       'ABAAEAAAICTAEAOw==';
 
   this.xhr_.onload = function() {};
   this.xhr_.abort();
 
   // Dispose memory allocated by Canvas.
   this.canvas_.width = 0;
   this.canvas_.height = 0;
 };