gpu: Yield from raster decoder after image uploads.

Have the RasterDecoder yield to allow interruption after image transfer
cache entry deserialization. Image uploads tend to be slow operations,
its good to yield after them to allow higher priority UI work to
proceed.

R=enne@chromium.org, piman@chromium.org

Bug: 970134
Change-Id: If0f488b7efc2c0eac559733333cf4de17882ab4a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1643087
Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: enne <enne@chromium.org>
Commit-Queue: Khushal <khushalsagar@chromium.org>
Auto-Submit: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#666162}