Fix accessibility issues in AudioPlayer and VideoPlayer.

ui/file_manager/file_manager/foreground/elements/files_icon_button.js

+// Copyright 2015 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.
+
+Polymer({
+  is: 'files-icon-button',
+
+  hostAttributes: {
+    role: 'button',
+    tabindex: 0
+  },
+
+  behaviors: [
+    Polymer.IronButtonState,
+    Polymer.IronControlState
+  ],
+
+  observers: [
+    '_focusedChanged(receivedFocusFromKeyboard)'
+  ],
+
+  _focusedChanged: function(receivedFocusFromKeyboard) {
+    if (receivedFocusFromKeyboard) {
+      this.classList.add('keyboard-focus');
+    } else {
+      this.classList.remove('keyboard-focus');
+    }
+  }
+});