GitLab

This patch ensures that we can generate discardable images metadata
whether we have picture caching enabled or we don't.

BUG=543208
R=pdr
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1397203003

Cr-Commit-Position: refs/heads/master@{#354124}