(This is a merge of http://go/wvgerrit/66625)
Google C++ Style dictates that methods which override base class or
interface methods should be declared "override" but not "virtual". Since
our codebase has not had access to "override" until now, many of our
classes do not follow this rule. I've updated as many places as I could
find to follow Google C++ Style, which should hopefully help us catch
errors better in the future.
Bug: 111851141
Test: CE CDM Unit Tests
Test: Android Unit Tests
Change-Id: Ic23e2e482e967256da306791532b5fec7b81b2f2
b771d93514