GitLab

A visibile to invisible state change will also release memory and should therefore wait as an unload does

A visibility change will also release memory and should therefore also stall an immediate unload.

Updated comments and cleaned up the ResourceManager function.

BUG=414918
TEST=unittest

Review URL: https://codereview.chromium.org/588823002

Cr-Commit-Position: refs/heads/master@{#296118}