This extends the existing clearing of type feedback cells during GC to
incremental marking in order to prevent cross-context retention that
would last until the next non-incremental GC.

R=erik.corry@gmail.com
TEST=cctest/test-heap/IncrementalMarkingClearsTypeFeedbackCells

Review URL: https://chromiumcodereview.appspot.com/10823082

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12245 ce2b1a6d-e550-0410-aec6-3dcde31c8c00