GitLab

- Lossless encode/color requests may be ignored by codecs.
- VideoEncoderVpx supports lossless color when using VP9.
- The --enable-i444 flag now controls the default color mode for VP9.

BUG=260879,134202

Review URL: https://codereview.chromium.org/304653002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@273752 0039d316-1c4b-4281-b951-d872f2087c98