Let WebSourceBufferImpl::setMode() update SourceState::sequence_mode_
Connects WebSourceBufferImpl::setMode() to similar ChunkDemuxer
and SourceState methods to enable setting SourceState::sequence_mode_.
Later changes will implement processing of distinct 'segments'
and 'sequence' append modes.
R=acolwell@chromium.org
TEST=On local Linux, all mediasource layout tests and media_unittests pass
BUG=249422
Review URL: https://codereview.chromium.org/
134883002
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244741 0039d316-1c4b-4281-b951-d872f2087c98