(This is a merge of http://go/wvgerrit/70666)
We need a reader-writer lock implementation in order to make use of the
new threading guarantees in OEMCrypto v15. However, we do not have
access to an STL reader-writer lock due to only being on C++11. This
patch adds a home-grown reader-writer lock, as well as tests to verify
that its behavior is sound.
Bug: 70889998
Bug: 118584039
Test: CE CDM Unit Tests
Test: Android Unit Tests
Change-Id: Iaddcefb50e72452fbd27d04879eacf775484e675
