This allows CompareICs to be cleared during garbage collection to avoid
cross-context garbage retention through maps stored in CompareIC stubs
for the KNOWN_OBJECTS state.

R=vegorov@chromium.org
BUG=v8:2102

Review URL: https://chromiumcodereview.appspot.com/10263008

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11491 ce2b1a6d-e550-0410-aec6-3dcde31c8c00