Merge from Widevine repo of http://go/wvgerrit/22804
Create a class, AuthenticationRoot, to encapsulate the objects and
logic for managing either keyboxes or certificates as the device's
root of trust.
Currently the class provides the existing keybox-related functions
needed by oemcrypto's CryptoEngine. It will be extended to provide
both keybox and certificate related functions, and the logic to
determine whether keybox or certificate based authentication should
be performed.
Change-Id: I792d1bfc8e9a81bbfd2baec20e3b3d182f0392f7
3164194908