Enable lossless colour by default.

This setting currently affects only sessions that use the VP9 encoding, causing them to default to the virtually-lossless I444 colour space, rather than to I420.

BUG=134202

Review URL: https://codereview.chromium.org/1199653003

Cr-Commit-Position: refs/heads/master@{#337923}
1 file changed