Reland "Replace reduce-memory mode in idle notification with delayed clean-up GC."

Reland "Replace reduce-memory mode in idle notification with delayed clean-up GC."

This reverts commit 269918927a54cd1533ef4e3318dd76b3747762b5.
This reverts commit 435b3c873ac3b58fb56a1b7292951810c93ceda5.

The failing test is fixing in chromium.

BUG=chromium:490559
LOG=NO
TBR=hpayer@chromium.org

Committed: https://crrev.com/a7f62edb7114604cc6a58f261923530299155f80
Cr-Commit-Position: refs/heads/master@{#29512}

[ulan, 2015-07-07 11:12:36]

ulan@chromium.org changed reviewers:
+ hpayer@chromium.org

[ulan, 2015-07-07 11:12:45]

The CQ bit was checked by ulan@chromium.org

[commit-bot: I haz the power, 2015-07-07 11:12:55]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1208993009/1

[commit-bot: I haz the power, 2015-07-07 11:37:50]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-07 11:38:04]

Patchset 1 (id:??) landed as
https://crrev.com/a7f62edb7114604cc6a58f261923530299155f80
Cr-Commit-Position: refs/heads/master@{#29512}