Implement NodeCache in terms of base::hash and std::equal_to in preparation
for HeapConstant caching.

TEST=cctest,unittests
R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/624153003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24412 ce2b1a6d-e550-0410-aec6-3dcde31c8c00