GitLab

Previously vp9 video was assumed to be in BT601. Now the vp9
color space flag is used to support BT709 as well.

BUG=447716
TEST=media_unittests --gtest_filter='PipelineIntegrationTest*'

Review URL: https://codereview.chromium.org/978483002

Cr-Commit-Position: refs/heads/master@{#319110}