media_controls: Add UI for showing a promo bubble on a control button.

third_party/WebKit/Source/core/css/mediaControlsAndroid.css

Index: third_party/WebKit/Source/core/css/mediaControlsAndroid.css
diff --git a/third_party/WebKit/Source/core/css/mediaControlsAndroid.css b/third_party/WebKit/Source/core/css/mediaControlsAndroid.css
index 5efa1b6f3d73b6c5771245f46c7ae8d94fd43d4e..e47c4dc48f293eae7af63f3d1fc3570887652fe5 100644
--- a/third_party/WebKit/Source/core/css/mediaControlsAndroid.css
+++ b/third_party/WebKit/Source/core/css/mediaControlsAndroid.css
@@ -35,7 +35,7 @@ audio::-webkit-media-controls-enclosure, video::-webkit-media-controls-enclosure
     min-width: 48px;
     /* This is a magic CSS entry to fix crbug.com/519557. Please don't change
      * without consulting that crbug. */
-    overflow: hidden;
+    overflow: visible;
 }
 
 audio::-webkit-media-controls-panel, video::-webkit-media-controls-panel {
@@ -64,6 +64,11 @@ audio::-webkit-media-controls-time-remaining-display, video::-webkit-media-contr
     height: 48px;
 }
 
+video::-internal-media-controls-download-button-container {
+    width: 48px;
+    height: 48px;
+}
+
 audio::-webkit-media-controls-play-button, video::-webkit-media-controls-play-button,
 audio::-webkit-media-controls-mute-button, video::-webkit-media-controls-mute-button,
 audio::-webkit-media-controls-fullscreen-button, video::-webkit-media-controls-fullscreen-button,