Revert of Replace reduce-memory mode in idle notification with delayed clean-up GC. (patchset #17 id:320001 of https://codereview.chromium.org/1218863002/)

Reason for revert:
[Sheriff] Looks like it blocks the roll (bisected). Speculative revert.
https://codereview.chromium.org/1210293003/

Original issue's description:
> Replace reduce-memory mode in idle notification with delayed clean-up GC.
>
> BUG=490559
> LOG=NO
>
> Committed: https://crrev.com/0ecd9e1bd2c6b519d4e7285f46cb7e844bc2235c
> Cr-Commit-Position: refs/heads/master@{#29451}

TBR=hpayer@chromium.org,ulan@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=490559

Review URL: https://codereview.chromium.org/1226703002

Cr-Commit-Position: refs/heads/master@{#29470}