Parallel compilation fix: the optimizer thread shouldn't change the allow allocation state on AssertNoAllocation scopes.

BUG=
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/14796014

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14551 ce2b1a6d-e550-0410-aec6-3dcde31c8c00