Plug some memory leaks in parser tests.

BUG=v8:2763
R=dslomov@chromium.org

Review URL: https://codereview.chromium.org/18694004

Patch from Sergey Matveev <earthdok@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15490 ce2b1a6d-e550-0410-aec6-3dcde31c8c00