Fix accessibility issues in AudioPlayer and VideoPlayer.

ui/file_manager/video_player/css/media_controls.css

 /* Copyright (c) 2012 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. */
 
 /* Common styles for media buttons. */
 
 .media-button {
   background-position: center;
   background-repeat: no-repeat;
   flex: none;
   height: 32px;
   position: relative;
   width: 32px;
 }
 
-.media-button:hover {
-  background-color: rgba(153, 153, 153, 0.2);
-}
-
-.media-button:active {
-  background-color: rgba(153, 153, 153, 0.4);
-}
-
 .media-button.disabled {
   background-color: transparent;
   opacity: 0.26;
 }
 
 .media-button.disabled,
 paper-slider[disabled],
 paper-slider.readonly {
   pointer-events: none;
 }
@@ skipping 122 matching lines @@
 
 /* Fullscreen button. */
 /* There is no final decision whether we need a separate icon when toggled. */
 
 .media-button.fullscreen {
   background-image: -webkit-image-set(
     url(../images/media/media_fullscreen.png) 1x,
     url(../images/media/2x/media_fullscreen.png) 2x);
 }
 
-#video-player[fullscreen] .media-button.fullscreen {
+#controls[fullscreen] .media-button.fullscreen {
   background-image: -webkit-image-set(
     url(../images/media/media_fullscreen_exit.png) 1x,
     url(../images/media/2x/media_fullscreen_exit.png) 2x);
 }
 
 .playback-state-icon {
   -webkit-animation: none;
   background-position: center center;
   background-repeat: no-repeat;
   display: none;
@@ skipping 72 matching lines @@
     url(../images/media/media_play_onscreen.png) 1x,
     url(../images/media/2x/media_play_onscreen.png) 2x);
 }
 
 .playback-state-icon[state='pause'] {
   -webkit-animation: blowup 500ms;
   background-image: -webkit-image-set(
     url(../images/media/media_pause_onscreen.png) 1x,
     url(../images/media/2x/media_pause_onscreen.png) 2x);
 }