GitLab

Make ClosedTabCache listen to MemoryPressure listener and
flush the cache if the memory pressure level is critical.

Design doc:
https://docs.google.com/document/d/1SF230MYWgroe4WikDMn82ETd3-HFRzylKtIk0HZRaOU/edit?usp=sharing

BUG=1100946

Change-Id: I73afb124ab596ae9bd9db1bed84684088c174096
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2352942Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Reviewed-by: Sreeja Kamishetty <sreejakshetty@chromium.org>
Commit-Queue: Andreea Bacanu <aebacanu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#800625}