Shrink allocatedObjectSizeThreshold for page navigation GC

Shrink allocatedObjectSizeThreshold for page navigation GC

This incrases the chance of a GC to be performed between tests and stablizes performance measurement for Speedometer.
https://257e68df4dae930120a4c67b6f7a507d5042fbc3-www.googledrive.com/host/0B4aiM9jljUy8UEh0QjR3SUVXaVE/linux-speedometer-0916-result.html

BUG=None

Committed: https://crrev.com/a8ec3a27c628e8e815b0b70a7d9455727669e115
Cr-Commit-Position: refs/heads/master@{#350498}

[keishi, 2015-09-24 06:04:53]

keishi@chromium.org changed reviewers:
+ haraken@chromium.org, oilpan-reviews@chromium.org

[keishi, 2015-09-24 06:04:53]

"Allocation threshold in a GC predicate should consider PartitionAlloc's memory
usage" CL doesn't look like it will help with speedometer.
https://257e68df4dae930120a4c67b6f7a507d5042fbc3-www.googledrive.com/host/0B4...

[haraken, 2015-09-24 06:06:32]

LGTM

[keishi, 2015-09-24 06:06:57]

The CQ bit was checked by keishi@chromium.org

[commit-bot: I haz the power, 2015-09-24 06:07:20]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1364183002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1364183002/1

[commit-bot: I haz the power, 2015-09-24 07:54:32]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-24 07:55:41]

Patchset 1 (id:??) landed as
https://crrev.com/a8ec3a27c628e8e815b0b70a7d9455727669e115
Cr-Commit-Position: refs/heads/master@{#350498}