Pass Isolate through CompilingCallsToThisStubIsGCSafe calls

BUG=v8:2487

Review URL: https://codereview.chromium.org/12732010

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13950 ce2b1a6d-e550-0410-aec6-3dcde31c8c00