Cherry-pick: Keep Compositor Offscreen context in sync compositor

Clean cherry-pick of crrev.com/r253081

Original description:

This is used as the share context for video on main thread. Until we can
properly clean up the video context, just skip releasing the this
context to avoid issues during mode switch.

BUG: 13328348

Change-Id: Ie0c10a932299f395c0acdac4c47477541aae0c51
2 files changed