Port r11491 (705d40cc)

Original commit message:
Implement clearing of CompareICs.

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.

BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/10342024
Patch from Akos Palfi <palfia@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11505 ce2b1a6d-e550-0410-aec6-3dcde31c8c00