GitLab

Previously we download one photo and display it and then discard the
photo. However when the access token expires, we cannot get photo link
info anymore. This patch saves previous downloaded photos to disk and
then cycle through those photos for a longer time span.

Bug: b/156919253
Test: new unittests
Change-Id: I6a0bd0b3f69e1e6c3d950c158960071dfce122c6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2207755
Commit-Queue: Tao Wu <wutao@chromium.org>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#784498}