DO NOT LAND MediaControls trybot run

Tweak the public/protected/private sections of MediaControls

After the merge this looked rather strange, so keep as public that
which is used by HTMLMediaElement or MediaControlElements, make
protected that which is used/overridden by MediaControlsAndroid, and
make everything else private.

BUG=341813
Make MediaControls minimally virtual

Only the functions which are overridden in MediaControlsAndroid need
be virtual.

updateStatusDisplay() didn't do anything, so it was removed.

BUG=341813
Rename MediaControlsChromiumAndroid to MediaControlsAndroid

BUG=341813
Merge MediaControlsChromium into MediaControls

To the largest extent possible, code was copied from
MediaControlsChromium.* to MediaControls.* without modification. Where
MediaControlsChromium virtual functions called the MediaControls base
functions, the order was preserved to avoid changing behavior.

BUG=341813