OEMCrypto Mock SRM functionality

Merge from Widevine repo of http://go/wvgerrit/24730

This CL adds SRM functionality to the modable version of oemcrypto
mock.  This can be used for end-to-end testing.

b/28955873
b/37353534

Change-Id: I2c6f513495ccfd42f7a3d7a3449db6f810563c04

libwvdrmengine/oemcrypto/mock/src/oemcrypto_key_mock.h

@@ -52,6 +52,7 @@ class KeyControlBlock {
   uint32_t nonce() const { return nonce_; }
   const char* verification() const { return verification_; }
   uint32_t control_bits() const { return control_bits_; }
+  void RequireLocalDisplay();
 
  private:
   uint32_t ExtractField(const std::vector<uint8_t>& str, int idx);