Add tests for SEA IR types infrastructure.

type_data_test.cc: Tests the type store used to record info on
                the types of results from instructions.
type_inferecen_visitor_test.cc: Tests type merging and related
                operations.
Android.gtest.mk: Included new tests.
type_inference_visitor.h/.cc: Marked function as const
                and made public.
scoped_hashtable_test.cc: Included full header path in #include.

Change-Id: I868461dcaed1e7f75db15958b83a3db7e17f6a64