Merge from Widevine repo of http://go/wvgerrit/24728
We use compiler options to set different properties in the oemcrypto
mock. With this CL, we define a base class that has default
properties. All other variants need only define the properties that
they change.
b/35141278
b/37353534
Change-Id: Id38ec5bf35dcd83cea9a066ebe201e6da7c1a2b0