Cleanup test-alloc unit test case.

Cleanup test-alloc unit test case.

This makes the test-alloc test case more robust against changes to the
initial heap size. It correctly simulates a full space now instead of
trying to fill the space up by allocating filler objects.

R=svenpanne@chromium.org
TEST=cctest/test-alloc

Committed: https://code.google.com/p/v8/source/detail?r=11284

[Sven Panne, 2012-04-12 10:03:28]

lgtm