GitLab

We had a number of different test SharedImageBackings. Centralize these
in one file.

Bug: 1003686
Change-Id: I09897394248a4aa560dffb84ce96f459db8d6821
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1974605
Commit-Queue: Eric Karl <ericrk@chromium.org>
Reviewed-by: vikas soni <vikassoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726980}