Adds keyboard functionality for videos.

third_party/WebKit/Source/core/html/shadow/MediaControls.h

 /*
  * Copyright (C) 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2011, 2012 Google Inc. All rights reserved.
  *
  * 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 101 matching lines @@
     refreshCastButtonVisibility();
   }
 
   // TODO(mlamouri): this method is needed in order to notify the controls that
   // the `mediaControlsEnabled` setting has changed.
   void onMediaControlsEnabledChange() {
     // There is no update because only the overlay is expected to change.
     refreshCastButtonVisibilityWithoutUpdate();
   }
 
+  void onMediaKeyboardEvent(Event* event) { defaultEventHandler(event); }

[mlamouri (slow - plz ping), 2017/03/27 13:02:12]

Can you move this in the block that starts with the "// Methods called by
MediaControlsMediaEventListener" comment?

Also maybe call it "onKeyPress" to make it generic. MediaControls could re-use
this for other stuff.

Finally, what about having our own handler for this with the `key` sent back.

[CJ, 2017/04/08 00:31:27]

Done.

+
   DECLARE_VIRTUAL_TRACE();
 
  private:
   friend class MediaControlsMediaEventListener;
   friend class MediaControlsOrientationLockDelegateTest;
   friend class MediaControlsTest;
 
   void invalidate(Element*);
 
   // Need to be members of MediaControls for private member access.
@@ skipping 101 matching lines @@
   IntSize m_size;
 
   bool m_keepShowingUntilTimerFires : 1;
 };
 
 DEFINE_ELEMENT_TYPE_CASTS(MediaControls, isMediaControls());
 
 }  // namespace blink
 
 #endif