Ash: Support "Next Song", "Previous Song", "Play/Pause" Multi Media buttons

chrome/common/extensions/api/media_player_private.json

 // 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.
 
 [
   {
     "namespace": "mediaPlayerPrivate",
     "nodoc": "true",
     "types": [
       {
@@ skipping 63 matching lines @@
         ]
       },
       {
         "name": "closeWindow",
         "description": "Closes the media player window.",
         "parameters": []
       }
     ],
     "events": [
       {
+        "name": "onNextTrack",
+        "type": "function",
+        "description": "Notifies that the next track was requested.",
+        "parameters": []
+      },
+      {
         "name": "onPlaylistChanged",
         "type": "function",
         "description": "Notifies that playlist content or state has been changed. Data could be retrieved via 'getPlaylist'.",
         "parameters": []
+      },
+      {
+        "name": "onPrevTrack",
+        "type": "function",
+        "description": "Notifies that the previous tack was requested.",
+        "parameters": []
+      },
+      {
+        "name": "onTogglePlayState",
+        "type": "function",
+        "description": "Notifies that a play/pause toggle was requested.",
+        "parameters": []
       }
     ]
   }
 ]