PPC: perf enhancement: Use larger heap page size on PPC.

PPC: perf enhancement: Use larger heap page size on PPC.

Revisit of https://codereview.chromium.org/910333004.

Use 4MB heap page size over the default of 1MB.

This change provides an improvement of 1.86% on the composite octane
benchmark score on PPC. This is 0.56% more than if --min_semi_space_size=4
was used to specify a 4MB heap page size.

Additionally, two more tests required modification to account for
configurable heap page size.

R=svenpanne@chromium.org, hpayer@chromium.org, danno@chromium.org, mbrandy@us.ibm.com, michael_dawson@ca.ibm.com
BUG=

Committed: https://crrev.com/bb3bb6b773dc91741f9386fca433b81ec02c72c6
Cr-Commit-Position: refs/heads/master@{#29775}

[Hannes Payer (out of office), 2015-07-21 06:52:25]

lgtm

[dstence, 2015-07-21 15:04:27]

The CQ bit was checked by dstence@us.ibm.com

[commit-bot: I haz the power, 2015-07-21 15:04:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1221433022/1

[commit-bot: I haz the power, 2015-07-21 15:52:09]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-21 15:52:24]

Patchset 1 (id:??) landed as
https://crrev.com/bb3bb6b773dc91741f9386fca433b81ec02c72c6
Cr-Commit-Position: refs/heads/master@{#29775}