Make TestInternalWeakLists more robust against flags.

Make TestInternalWeakLists more robust against flags.

This makes some tests in test-heap.cc more robust against flags, now
that top-level code can be optimized by the --always-opt flag.

R=hpayer@chromium.org
TEST=cctest/test-heap/TestInternalWeakLists

Committed: https://crrev.com/63eeab12ebe69722a9bfbc7fa4ea893ca352d7bb
Cr-Commit-Position: refs/heads/master@{#27699}

[Hannes Payer (out of office), 2015-04-09 10:58:51]

lgtm

[Michael Starzinger, 2015-04-09 11:00:00]

The CQ bit was checked by mstarzinger@chromium.org

[commit-bot: I haz the power, 2015-04-09 11:00:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1071063004/1

[commit-bot: I haz the power, 2015-04-09 11:01:24]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-09 11:01:37]

Patchset 1 (id:??) landed as
https://crrev.com/63eeab12ebe69722a9bfbc7fa4ea893ca352d7bb
Cr-Commit-Position: refs/heads/master@{#27699}