Graphs:
https://uma.googleplex.com/p/chrome/timeline_v2/?sid=6d95730b5c28f6d76bbb58911796b1f6


There is a 4MB spike on Discarable memory usage. Though the discardable manager allocates segments in 4MB chunks, this does look like a regression.

I suspect this change caused the regression.

commit dab7ed26d647862149d4c4b5e6d044fbe235571e
Author: Eric Karl <ericrk@chromium.org>
Date:   Fri Aug 31 19:57:40 2018 +0000

    Re-land: Hold pre-decoded images until use or 250ms rather than 2 frames



Other less probable suspects:
https://chromium-review.googlesource.com/1159203
https://chromium-review.googlesource.com/1180658