Revert of Remove redundant activation threshold for incremental marking.

Revert of Remove redundant activation threshold for incremental marking. (patchset #1 id:1 of https://codereview.chromium.org/1418293006/ )

Reason for revert:
Regression in thread_times.key_idle_power_cases (crbug.com/555153)

Original issue's description:
> Remove redundant activation threshold for incremental marking.
>
> The minimum allocation limit already enforces this constraint for normal GCs.
>
> GCs triggered by the memory reducer and external limit should work for all heap sizes.
>
> BUG=chromium:552305
> LOG=NO
>
> Committed: https://crrev.com/e28e4d5f52852e2f14facc37a02069b6bfc82c4e
> Cr-Commit-Position: refs/heads/master@{#31921}

TBR=hpayer@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:552305
Committed: https://crrev.com/401efe2173b1d777634996817bf85fe3bde434f0
Cr-Commit-Position: refs/heads/master@{#32038}

[ulan, 2015-11-17 13:12:52]

Created Revert of Remove redundant activation threshold for incremental marking.

[commit-bot: I haz the power, 2015-11-17 13:12:56]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1456523002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1456523002/1

[commit-bot: I haz the power, 2015-11-17 13:13:07]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-17 13:13:50]

Patchset 1 (id:??) landed as
https://crrev.com/401efe2173b1d777634996817bf85fe3bde434f0
Cr-Commit-Position: refs/heads/master@{#32038}