MSE: Test append window discontinuity detection

MSE: Test append window discontinuity detection

In both sequence and segments append modes, no discontinuity processing should
occur if append window filtering drops no more than two full frame durations
plus any partial frame discards since the track buffer's last decode timestamp.
Discontinuity processing should occur otherwise.
This change includes unit tests for these cases, and notes some curious
compliant sequence mode discontinuity detection behavior.

R=acolwell@chromium.org
BUG=249422
TEST=new unit test

[wolenetz, 2014-05-31 01:11:27]

PTAL @ PS2 on your return:

w.r.t. strange compliant sequence mode (lack of) discontinuity detection, ISTM
this is by-design in the spec. WDYT? I have not filed either a crbug or w3c bug
yet.

Here's some detail on how large gaps in buffered ranges can be introduced in
contiguous appends in sequence mode, with append window filtering:

SequenceMode/AudioOnly_AppendWindowAndMinimalDiscontinuity :

frame_processor.cc(24)] SetSequenceMode(1)
frame_processor.cc(101)] ProcessFrame: Processing frame Type=1, TrackID=-2,
PTS=0, DTS=0, DUR=0.01
frame_processor.cc(149)] ProcessFrame: updated timestampOffset is now 0 
frame_processor_base.cc(91)] NotifyNewMediaSegmentStarting(0)
chunk_demuxer.cc(846)] ChunkDemuxerStream::OnNewMediaSegment(0)
frame_processor.cc(333)] ProcessFrame: Sending processed frame to stream, PTS=0,
DTS=0
frame_processor.cc(101)] ProcessFrame: Processing frame Type=1, TrackID=-2,
PTS=0.01, DTS=0.01, DUR=0.01
frame_processor.cc(333)] ProcessFrame: Sending processed frame to stream,
PTS=0.01, DTS=0.01
frame_processor.cc(101)] ProcessFrame: Processing frame Type=1, TrackID=-2,
PTS=0.02, DTS=0.02, DUR=0.01
frame_processor.cc(296)] Dropping frame that is outside append window.
frame_processor.cc(101)] ProcessFrame: Processing frame Type=1, TrackID=-2,
PTS=0.03, DTS=0.03, DUR=0.01
frame_processor.cc(296)] Dropping frame that is outside append window.
frame_processor.cc(101)] ProcessFrame: Processing frame Type=1, TrackID=-2,
PTS=0.04, DTS=0.04, DUR=0.01
frame_processor.cc(225)] ProcessFrame : Sequence mode discontinuity, GETS: 0.02
frame_processor_base.cc(74)] Reset()
frame_processor_base.cc(26)] Reset()
frame_processor.cc(236)] ProcessFrame: Discontinuity: reprocessing frame
frame_processor.cc(101)] ProcessFrame: Processing frame Type=1, TrackID=-2,
PTS=0.04, DTS=0.04, DUR=0.01
frame_processor.cc(149)] ProcessFrame: updated timestampOffset is now -0.02

*******
No further discontinuity can be detected until track buffer gets another
surviving frame, since track buffer's last decode timestamp remains unset since
last discontinuity. So timestampOffset does not get updated further, and a gap
at least as large as 2 * last frame duration is introduced.
*******

frame_processor.cc(296)] Dropping frame that is outside append window.
frame_processor.cc(101)] ProcessFrame: Processing frame Type=1, TrackID=-2,
PTS=0.05, DTS=0.05, DUR=0.01
frame_processor.cc(296)] Dropping frame that is outside append window.
frame_processor.cc(101)] ProcessFrame: Processing frame Type=1, TrackID=-2,
PTS=0.06, DTS=0.06, DUR=0.01
frame_processor.cc(333)] ProcessFrame: Sending processed frame to stream,
PTS=0.04, DTS=0.04
frame_processor.cc(101)] ProcessFrame: Processing frame Type=1, TrackID=-2,
PTS=0.07, DTS=0.07, DUR=0.01
frame_processor.cc(333)] ProcessFrame: Sending processed frame to stream,
PTS=0.05, DTS=0.05
frame_processor_unittest.cc(248)] StoreStatusAndBufferstatus: 0 ts: 0
frame_processor_unittest.cc(248)] StoreStatusAndBufferstatus: 0 ts: 0.01
frame_processor_unittest.cc(248)] StoreStatusAndBufferstatus: 0 ts: 0.04
frame_processor_unittest.cc(248)] StoreStatusAndBufferstatus: 0 ts: 0.05
frame_processor.cc(20)] ~FrameProcessor