Implement provisioning 3.0 functionality in oemcrypto mock

Merge from widevine repo of http://go/wvgerrit/21684

This CL adds provisioning 3.0 functionality to the OEMCrypto reference
implementation.

Change-Id: I60c1fd88f246d443e0ae59ad56862c2ea9d95445

libwvdrmengine/oemcrypto/mock/src/oemcrypto_engine_device_properties.cpp

@@ -38,6 +38,17 @@ bool CryptoEngine::supports_keybox() {
   return true;
 }
 
+// This version uses a keybox.
+OEMCrypto_ProvisioningMethod CryptoEngine::provisioning_method() {
+  return OEMCrypto_Keybox;
+}
+
+OEMCryptoResult CryptoEngine::get_oem_certificate(SessionContext *session,
+                                                  uint8_t *public_cert,
+                                                  size_t *public_cert_length) {
+  return OEMCrypto_ERROR_NOT_IMPLEMENTED;
+}
+
 // Returns false for mock library to indicate the client does not support
 // anti-rollback hardware.
 bool CryptoEngine::is_anti_rollback_hw_present() {