Summary:
Whenever a Java class implements equals(), it has to implement hashCode(), otherwise
there might be weird behavior when inserting instances of the class in a hash map for
example. This adds two missing hashCode() implementations and extends tests to test
the hashCode() implementations.
Test Plan: make jtest
Reviewers: rven, igor, sdong, yhchiang
Reviewed By: yhchiang
Subscribers: anthony, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D43017
6a82fba75f