mojo: Make EqualsTraits<> part of public C++ API
Users of mapped types sometimes need to provide their own custom
comparsion functions for classes that do not provide operator==() or an
Equals() method. Move EqualsTraits<> out of mojo internals, similar to
how CloneTraits<> is handled.
BUG=714689
TEST=compiles
Review-Url: https://codereview.chromium.org/2837353002
Cr-Commit-Position: refs/heads/master@{#467160}
CrOS-Libchrome-Original-Commit: b9404e80f80b4bddfa2c24ca042393ceb5a5b882
5 files changed