Restore capacity increase on underflow for MSE playbacks.

The "increase preroll capacity on underflow" logic was disabled for MSE
playbacks a while ago because it was causing unwanted garbage
collections and was allowing the capacity to grow too large. This change
restores the capacity increase logic, but restricts the capacity so that
it never grows beyond 3 seconds worth of data. This will avoid the GC
issues encountered before.

This change also resets the capacity on flush so that capacity increases
in one playback period don't negatively effect the seek start time.


BUG=291726
TEST=AudioRendererImplTest.Underflow, AudioRendererImplTest.Underflow_FollowedByFlush

Review URL: https://codereview.chromium.org/88743004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238230 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238230