VAVDA: Remove dead code and don't call client if it's invalidated.

Remove a few lines of unused code from VAVDA.

Also, ensure the client_ hasn't been invalidated before calling methods on it directly.

BUG=None
TEST=build, video playback

Review URL: https://codereview.chromium.org/110073003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241774 0039d316-1c4b-4281-b951-d872f2087c98
Add Web MIDI chrome::flags switch for Android

The actual Web MIDI implementation is not yet done.

R=toyoshim@chromium.org
BUG=303596

Review URL: https://codereview.chromium.org/111293003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241775 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241775