Move policy validation for unoptimized-images and legacy-formats to image loader

To avoid image policy validated / reported multiple times, this CL
moves the validation of non-layout-dependant policies to image loader
ImageNotifyFinished so that the validatiom will only happen once per
image load.

Bug: 926199
Change-Id: I3ec2b8da16e8719f73d09e6feba8dddbba7059d1
Reviewed-on: https://chromium-review.googlesource.com/c/1446065
Commit-Queue: Luna Lu <loonybear@chromium.org>
Reviewed-by: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#630926}
9 files changed