Hashmaps with a simple key equality method (comparing pointers) don't
need to waste cycles (and branches) comparing hash values, as the key
comparison is cheap.

This patch modifies the hashmap's MatchFun to take the hashes as well as
the keys, thus allowing the MatchFun to ignore the hashes. This allows
slightly cleaner generated code, especially when the MatchFun is
inlined.

BUG=

Review-Url: https://codereview.chromium.org/2381303002
Cr-Commit-Position: refs/heads/master@{#39932}