Fix GPU explicit resource allocation bug

The explicit resource allocator assumes that it has complete control
over the resources it hands out thus, they can have no pre-existing
pending IO.

Change-Id: I59d8d079d8b8514688c458a54424329b86922cb6
Reviewed-on: https://skia-review.googlesource.com/143300
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
7 files changed