Fix typo in assert.

Fix typo in assert.
Also remove the requirement to have an AssertNoAllocation object when getting the flat content. We actually do allow allocation, it's just GC's we don't allow.

Review URL: http://codereview.chromium.org/7710018

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9001 ce2b1a6d-e550-0410-aec6-3dcde31c8c00