Avoid unnecessary hashing in OrderedHashTable

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

Committed: https://code.google.com/p/v8/source/detail?r=22308

[Michael Starzinger, 2014-07-09 07:41:56]

LGTM.

[adamk, 2014-07-09 16:19:59]

Committed patchset #1 manually as r22308 (presubmit successful).