Add subtitles track if there is a subtitles file with the same name.

ui/file_manager/video_player/js/video_player.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 {!HTMLElement} playerContainer Main container.
  * @param {!HTMLElement} videoContainer Container for the video element.
  * @param {!HTMLElement} controlsContainer Container for video controls.
  * @constructor
  * @struct
@@ skipping 358 matching lines @@
               this.controls.attachMedia(this.videoElement_);
             }.bind(this));
           }.bind(this));
     } else {
       metrics.recordPlayType(metrics.PLAY_TYPE.LOCAL);
       videoPlayerElement.removeAttribute('casting');
 
       this.videoElement_ = document.createElement('video');
       getRequiredElement('video-container').appendChild(this.videoElement_);
 
+      var videoUrl = video.toURL();
       this.controls.attachMedia(this.videoElement_);
-      this.videoElement_.src = video.toURL();
+      var source = document.createElement('source');
+      source.src = videoUrl;
+      this.videoElement_.appendChild(source);
 
       media.isAvailableForCast().then(function(result) {
         if (result)
           videoPlayerElement.setAttribute('castable', true);
         else
           videoPlayerElement.removeAttribute('castable');
       }).catch(function() {
         videoPlayerElement.setAttribute('castable', true);
       });
 
-      videoElementInitializePromise = Promise.resolve();
+      videoElementInitializePromise = this.loadSubtitles_(videoUrl)
+          .then(function(subltitleUrl) {
+            if (subltitleUrl) {
+              var track = document.createElement('track');
+              track.src = subltitleUrl;
+              track.kind = 'subtitles';
+              track.default = true;
+              this.videoElement_.appendChild(track);
+            }
+            return Promise.resolve();

[yoshiki, 2016/03/14 04:10:52]

nit: returning resolve is unnecessary. please remove.

[ryoh, 2016/03/14 13:45:25]

Done.

+          }.bind(this));
     }
-
     videoElementInitializePromise
         .then(function() {
           var handler = function(currentPos) {
             if (currentPos === this.currentPos_) {
               if (opt_callback)
                 opt_callback();
               videoPlayerElement.removeAttribute('loading');
             }
 
             this.videoElement_.removeEventListener('loadedmetadata', handler);
           }.wrap(this, this.currentPos_);
 
           this.videoElement_.addEventListener('loadedmetadata', handler);
 
           this.videoElement_.addEventListener('play', function() {
             chrome.power.requestKeepAwake('display');
             this.updateInactivityWatcherState_();
           }.wrap(this));
           this.videoElement_.addEventListener('pause', function() {
             chrome.power.releaseKeepAwake();
             this.updateInactivityWatcherState_();
           }.wrap(this));
 
-          this.videoElement_.load();

[ryoh, 2016/03/11 15:11:58]

Why do we need this line?
It seems 'loadedmetadata' event will be fired whether we call this function or
not.
If you call this function here, we can't see subtitles.
(I think it might be a bug of blink)

[yoshiki, 2016/03/14 04:10:52]

According to the spec, we need to call load() unless 'src' attribute on
'video'-tag element is modified.
https://dev.w3.org/html5/spec-author-view/video.html
So, I think we should do this.

However, even if the video player works correctly without this, you may remove
it but please leave the comment.

And if you think it's a bug, please file a bug to http://crbug.com/new. Thanks.

[ryoh, 2016/03/14 13:45:25]

Yeah, if we **modified** src attribute, you have to call load(), but we always
create new 'video' element (IIRC).
Maybe we don't have to call load().

OK, I reported this as a bug:
https://bugs.chromium.org/p/chromium/issues/detail?id=594537

           callback();
         }.bind(this))
         // In case of error.
         .catch(function(error) {
           if (this.currentCast_)
             metrics.recordCastVideoErrorAction();
 
           videoPlayerElement.removeAttribute('loading');
           console.error('Failed to initialize the video element.',
                         error.stack || error);
           this.controls_.showErrorMessage(
               'VIDEO_PLAYER_VIDEO_FILE_UNSUPPORTED');
           callback();
         }.bind(this));
   }.wrap(this));
 };
 
+VideoPlayer.prototype.loadSubtitles_ = function(url) {

[yoshiki, 2016/03/14 04:10:52]

nit: Please write a JSdoc (short description of the method and parameter).

[ryoh, 2016/03/14 13:45:25]

Done.

+  var baseUrl = util.splitExtension(url)[0];
+  var resolveLocalFileSystem = function(extension) {

[yoshiki, 2016/03/14 04:10:52]

"resolveLocalFileSystem" looks confusing with resolveLocalFileSystemURL().
"resolveLocalFileSystemWIthExtension" might be better?

[ryoh, 2016/03/14 13:45:25]

Sounds nice! Thank you.

+    return new Promise(
+        window.webkitResolveLocalFileSystemURL.bind(null, baseUrl + extension));
+  }

[yoshiki, 2016/03/14 04:10:52]

nit: semicolon

[ryoh, 2016/03/14 13:45:25]

Done.

+  return resolveLocalFileSystem('.vtt').then(function(subtitle) {
+    return subtitle.toURL();
+  }).catch(function() {
+    return '';
+  });
+};
+
 /**
  * Plays the first video.
  */
 VideoPlayer.prototype.playFirstVideo = function() {
   this.currentPos_ = 0;
   this.reloadCurrentVideo(this.onFirstVideoReady_.wrap(this));
 };
 
 /**
  * Unloads the current video.
@@ skipping 260 matching lines @@
   return new Promise(function(fulfill, reject) {
     util.URLsToEntries(window.appState.items, function(entries) {
       metrics.recordOpenVideoPlayerAction();
       metrics.recordNumberOfOpenedFiles(entries.length);
 
       player.prepare(entries);
       player.playFirstVideo(player, fulfill);
     }.wrap());
   }.wrap());
 }.wrap());