Add filler at the new space top when forcing scavenge.

Add filler at the new space top when forcing scavenge.

We only seem to force scavenge in our cctest test suite, so this is
expected to fix some flakiness in our tests, but it will not
improve stability of v8 itself.

R=hpayer@chromium.org
BUG=

Committed: https://code.google.com/p/v8/source/detail?r=19460

[Hannes Payer (out of office), 2014-02-18 09:39:13]

I think the problem is the PerformScavenge call, which avoids the main gc
selection logic and directly tries to invoke the scavenger.

I would suggest changing PerformScavenge to
void Heap::PerformScavenge() {
  CollectGarbage(NEW_SPACE, "try to invoke Scavenge directly");
}

or remove PerformScavenge and invoke CollectGarbage from the tests directly.

[Hannes Payer (out of office), 2014-02-18 11:41:03]

LGTM, one nit

https://codereview.chromium.org/167423004/diff/50001/test/cctest/test-memento...
File test/cctest/test-mementos.cc (right):

https://codereview.chromium.org/167423004/diff/50001/test/cctest/test-memento...
test/cctest/test-mementos.cc:66:
heap->CollectAllGarbage(Heap::kAbortIncrementalMarkingMask);
Change it to
CcTest::i_isolate()->heap()->CollectAllGarbage(Heap::kAbortIncrementalMarkingMask);

[Jarin, 2014-02-18 16:35:11]

Committed patchset #2 manually as r19460 (presubmit successful).