Re-apply "InstrProf: Use a test fixture in the coverage mapping tests"

Re-apply "InstrProf: Use a test fixture in the coverage mapping tests"

This time we use a helper to format the assertion so we can just use
ASSERT_TRUE instead of relying on ASSERT_EQ being able to deal with
conversions between enum types.

This reverts r229496, re-applying r229473.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229547 91177308-0d34-0410-b5e6-96231b3b80d8