Avoid unnecessary hashing in OrderedHashTable

Add an overload of OrderedHashTable::FindEntry that takes
a hash along with the key to allow callsites which need to
re-use the hash (such as Add()) to avoid recomputing it.

On my Macbook this results in improvements on the Collections
microbenchmarks:
  Map-Collections: +4%
  Set-Collections: +5%

R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/373323002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22308 ce2b1a6d-e550-0410-aec6-3dcde31c8c00