Rest of merge of http://go/wvgerrit/67884
Some files were deleted on original CL that were not deleted here.
Now that we can use C++11, we should use the cross-platform std::mutex
type, not the custom pthread version.
Bug: 111850982
Test: WV unit/integration tests
Change-Id: I48a1e47aa79e5e66b5869c0f766c18d561d26784