Cherry-pick: gpu: Use a single container for GLInProcessContext share group

Cherry-pick with conflict of crrev.com/r250765

Conflicts:
	gpu/command_buffer/service/in_process_command_buffer.cc

Original description:

Instead of having two global containers for GLInProcessContext
and InProcessCommandBuffer, use a single one for the former
and pass in the service-side share group while we are holding the
lock anyways.

This makes it simpler to support multiple service threads.

BUG: 13328348

Change-Id: Ia6d5817688e90cbd00d9cc6077d82e59c3933a0d
3 files changed