[heap] Extend mutex guards for CodeRange.

[heap] Extend mutex guards for CodeRange.

Previously the mutex only guarded free_list_. The extension covers also
allocation_list_.

BUG=chromium:524425
LOG=N

Committed: https://crrev.com/2c17f1580b0b62d01dc2f874dfff7041fc403990
Cr-Commit-Position: refs/heads/master@{#30748}

[Michael Lippautz, 2015-09-15 12:21:17]

The CQ bit was checked by mlippautz@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-09-15 12:21:29]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1341293002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1341293002/1

[Michael Lippautz, 2015-09-15 12:46:57]

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

[Michael Lippautz, 2015-09-15 12:46:57]

This is another spinoff from the prototype. Basically CodeRange::ReserveBlock is
potentially called concurrently. This means that for parallel compaction we
require guarding of allocation_list_ AND free_list_.

I merged the mutexes to avoid complexity (nested mutex). I would not expect the
performance impact to be noticeable.

[commit-bot: I haz the power, 2015-09-15 13:21:40]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-15 13:21:40]

Dry run: This issue passed the CQ dry run.

[Hannes Payer (out of office), 2015-09-15 13:41:30]

lgtm

[Michael Lippautz, 2015-09-15 13:43:58]

The CQ bit was checked by mlippautz@chromium.org

[commit-bot: I haz the power, 2015-09-15 13:44:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1341293002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1341293002/1

[commit-bot: I haz the power, 2015-09-15 13:45:23]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-15 13:45:39]

Patchset 1 (id:??) landed as
https://crrev.com/2c17f1580b0b62d01dc2f874dfff7041fc403990
Cr-Commit-Position: refs/heads/master@{#30748}