Add download button to MediaDocument on Android.

third_party/WebKit/LayoutTests/VirtualTestSuites

 [
   {
     "prefix": "gpu",
     "base": "fast/canvas",
     "args": ["--enable-accelerated-2d-canvas",
              "--disable-display-list-2d-canvas"]
   },
   {
     "prefix": "display_list_2d_canvas",
     "base": "fast/canvas",
@@ skipping 80 matching lines @@
     "prefix": "android",
     "base": "fullscreen",
     "args": ["--enable-threaded-compositing",
              "--enable-fixed-position-compositing", "--enable-prefer-compositing-to-lcd-text",
              "--enable-composited-scrolling-for-frames", "--enable-gesture-tap-highlight", "--enable-pinch",
              "--force-overlay-fullscreen-video", "--enable-overlay-scrollbars", "--enable-overscroll-notifications",
              "--enable-fixed-layout", "--enable-viewport", "--disable-canvas-aa",
              "--disable-composited-antialiasing"]
   },
   {
+    "prefix": "android",
+    "base": "media/mediadocument",
+    "args": ["--enable-features=MediaDocumentDownloadButton"]
+  },
+  {
     "prefix": "stable",
     "base": "fast/css3-text/css3-text-decoration/stable",
     "args": ["--stable-release-mode"]
   },
   {
     "prefix": "stable",
     "base": "web-animations-api",
     "args": ["--stable-release-mode"]
   },
   {
@@ skipping 126 matching lines @@
     "prefix": "scalefactor150",
     "base": "fast/hidpi/static",
     "args": ["--force-device-scale-factor=1.5"]
   },
   {
     "prefix": "scalefactor200withzoom",
     "base": "fast/hidpi/static",
     "args": ["--force-device-scale-factor=2", "--enable-use-zoom-for-dsf"]
   }
 ]