ClearTypeFeedbackInfo() assumed we have a context in the isolate.

Better, is to compare against the context for the JSFunction we are
currently looking at.

TBR=ulan@chromium.org

Review URL: https://codereview.chromium.org/294903013

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21440 ce2b1a6d-e550-0410-aec6-3dcde31c8c00