Document some of the implications of using MediaCodec and ref internal bugs.

Comment-only change that means I can reclaim some neurons instead of remembering
these things in some vague form until next time I forget them.

NOTRY=true

Review URL: https://codereview.chromium.org/99133004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239297 0039d316-1c4b-4281-b951-d872f2087c98
IndexedDB: Make deleteDatabase and getDatabaseNames close backing store

The factory opens up the backing store for the delete and enumerate
operations, but wasn't triggering the "lazily release the backing store"
mechanism when done since there's no database connection being closed.

BUG=325820
R=dgrogan@chromium.org,alecflett@chromium.org

Review URL: https://codereview.chromium.org/100213004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239298 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239298
Add UMA stats for Widevine key system support.

This indirectly provides stats for CanPlayType(<type>, widevine).
The stats are recorded by RecordComputedAction() in user_metrics.cc.

BUG=324927
TEST=Tested in JS console with document.createElement('video').canPlayType(...);

Review URL: https://codereview.chromium.org/100483004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239299 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239299