Because we run all tests three times with different variant flags (to
test crankshaft) we might end up in a situation where we try to write
to the same serilization file from two different threads
simultaneously. The patch concats the variant flags at the end of the
serialization file name.
Review URL: http://codereview.chromium.org/6688068

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7285 ce2b1a6d-e550-0410-aec6-3dcde31c8c00