Speculative fix for stack overflow in CollectEvacuationCandidates

Speculative fix for stack overflow in CollectEvacuationCandidates

I don't have a repro, but it seems that when we are close to the stack limit,
CollectEvacuationCandidates' local variables can blow the limit. To avoid
this, instead of always allocating a 2000-pointer-sizes array on the stack,
use a std::vector (which stores its elements on the heap), and while we're
at it, only allocate as many elements as we actually need.

Committed: https://crrev.com/052924abe3fb44df588f6e7c7df9ca691bbfa887
Cr-Commit-Position: refs/heads/master@{#27742}

[Jakob Kummerow, 2015-04-10 10:43:35]

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

[Jakob Kummerow, 2015-04-10 10:43:36]

As discussed. PTAL.

[Hannes Payer (out of office), 2015-04-10 11:00:15]

lgtm

[Jakob Kummerow, 2015-04-10 11:01:25]

The CQ bit was checked by jkummerow@chromium.org

[commit-bot: I haz the power, 2015-04-10 11:01:36]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1073123002/1

[commit-bot: I haz the power, 2015-04-10 11:24:30]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-10 11:24:35]

Patchset 1 (id:??) landed as
https://crrev.com/052924abe3fb44df588f6e7c7df9ca691bbfa887
Cr-Commit-Position: refs/heads/master@{#27742}