This fixes numerous audio/video synchronization issues caused by PtsHeap getting out of sync due to the decoder silently dropping/reordering frames.

Most decoder libraries (including FFmpeg and OpenMAX) feature some form of presentation timestamp reordering.  This is the first step in moving away from using PtsHeap and instead requireing VideoDecodeEngines + their libraries to handle presentation timestamp reordering.

This change also removes VideoFrame::GetRepeatCount() as it is an FFmpeg-specific detail.  The duration is now properly calculated inside FFmpegVideoDecodeEngine.

BUG=26036
TEST=videos linked in bugs remain in sync, as do all other videos

Review URL: http://codereview.chromium.org/1726015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@45856 0039d316-1c4b-4281-b951-d872f2087c98