The new string describes profile, level, bitdepth, color primaries,
eotf, matrix coefficients, full-range enable/disable, and chroma
subsampling.

Example:

  MediaSource.isTypeSupported(
    'video/webm; codecs="vp09.02.01.10.09.01.09.01.01"')

Ordering and required feilds are still under discussion, but this
reflects the latest proposal.

For HDR EOTFs (e.g. SMPTEST2084) canPlayType/isTypeSupported will
return ""/false until RenderMediaClient is made aware of whether
chrome is running with hdr output enabled.

To enable parsing of the new vp9 string in webm, use the flag
--enable-new-vp9-codec-string.

Alternatively, to enable HDR AND new vp9 string in webm, use
--enable-hdr-output

To enable parsing (and demuxing) of vp9 in mp4, use the flag
--enable-vp9-in-mp4

BUG=687627

Review-Url: https://codereview.chromium.org/2723833002
Cr-Commit-Position: refs/heads/master@{#455548}