Support loads from primitive values.
This also changes load computation to use HeapTypes rather than Maps.
TODO: move conversion between maps and heaptypes earlier in the process, already in the oracle.

BUG=
R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/147763006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18938 ce2b1a6d-e550-0410-aec6-3dcde31c8c00