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

Review URL: https://chromiumcodereview.appspot.com/10071003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11284 ce2b1a6d-e550-0410-aec6-3dcde31c8c00