into C++ without having a valid stack frame that can be
traversed at GC.
Also add asserts to track that we do not try to generate a stub
while we are generating a stub, since the stub creation code is
not GC safe.
Review URL: http://codereview.chromium.org/7084032

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8122 ce2b1a6d-e550-0410-aec6-3dcde31c8c00