Add download button to MediaDocument on Android.

third_party/WebKit/Source/core/css/mediaControls.css

 /*
  * Copyright (C) 2009 Apple Inc.  All rights reserved.
  * Copyright (C) 2009 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 71 matching lines @@
     bottom: auto;
     height: 30px;
     background-color: rgba(20, 20, 20, 0.8);
     border-radius: 5px;
     /* The duration is also specified in MediaControlElements.cpp and LayoutTests/media/media-controls.js */
     transition: opacity 0.3s;
 }
 
 video:-webkit-full-page-media {
     margin: auto;
-    position: absolute;
     top: 0;
     right: 0;
     bottom: 0;
     left: 0;
 }
 
 audio:-webkit-full-page-media, video:-webkit-full-page-media {
     max-height: 100%;
     max-width: 100%;
 }
@@ skipping 311 matching lines @@
     font-weight: bold;
 }
 
 video::cue(u) {
     text-decoration: underline;
 }
 
 video::cue(i) {
     font-style: italic;
 }