Clang-tidy google-readability-function check: don't warn on gmock
testing::Unused parameters.

Reviewers: bkramer, klimek

Reviewed By: klimek

Subscribers: curdeius, cfe-commits

Differential Revision: http://reviews.llvm.org/D5479

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@218443 91177308-0d34-0410-b5e6-96231b3b80d8