Cherry-pick: gpu: Avoid unbounded idle queue in in-process context

Clean cherry-pick of

BUG: 16550863

Original description:

Before this, a task is added to the idle queue each time in flush and
ScheduleMoreIdleWork. This means that as long as there is idle work, the
size of the queue grows by one in each flush.

Fix this by not adding any idle tasks if there is already one pending.

Change-Id: I77834205d3746e5ac43a804ec9ec173b0c372e6b
2 files changed