Reapply: Add Oilpan HeapContainsCache, HeapStats, FreeListEntry, HeapPage,
ThreadHeap and Visitor.

Stub out parts of the implementation to not have to drag in even more.

BUG=

Review URL: https://codereview.chromium.org/118243002

git-svn-id: svn://svn.chromium.org/blink/trunk@164100 bbb929c8-8fbe-4397-9dbb-9b2b20218538