MSE: Log to chrome://media-internals the buffering API being used

Logs either "ChunkDemuxer: buffering by PTS" or ... "by DTS" to
chrome://media-internals on MSE demuxer construction. This assists in
manual verification and debugging.

Tested with/without --enable-features=MseBufferByPts in cmdline

BUG=718641

Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I418fb8e9d89bbfc98c343b2db6effc8a03201794
Reviewed-on: https://chromium-review.googlesource.com/689865
Commit-Queue: Matthew Wolenetz <wolenetz@chromium.org>
Reviewed-by: Dan Sanders <sandersd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#505245}
3 files changed