Update OEMCrypto calls to use substrings

Merge from master branch of Widevine repo of http://go/wvgerrit/66073
Merge from oemcrypto-v15 branch of Widevine repo of http://go/wvgerrit/64083

As part of the update to v15, LoadKeys, RefreshKeys, and
LoadEntitledContentKeys should all use offsets and lengths into the
message rather than a pointer for its parameters. The CDM, tests,
adapters, and OEMCrypto implementations are changed to reflect this.

Test: tested as part of http://go/ag/5501993
Bug: 115874964

Change-Id: I981fa322dec7c565066fd163ca5775dbff71fccf

libwvdrmengine/cdm/core/include/crypto_session.h

@@ -32,6 +32,9 @@ void GenerateMacContext(const std::string& input_context,
 void GenerateEncryptContext(const std::string& input_context,
                             std::string* deriv_context);
 size_t GetOffset(std::string message, std::string field);
+OEMCrypto_Substring GetSubstring(const std::string& message = "",
+                                 const std::string& field = "",
+                                 bool set_zero = false);
 OEMCryptoCipherMode ToOEMCryptoCipherMode(CdmCipherMode cipher_mode);
 
 class CryptoSessionFactory;