Update copyright notice and fix entitlement key sizes

This change updates the copyright notice to make it more clear that
the code is distribued under the Widevine Master License Agreement.

It also updates the unit tests and sample code to correct the useage
of AES 256.  AES 256 is used to decrypt entitled content keys, but it
is not used to decrypt key control blocks.

test/oec_session_util.h

@@ -1,7 +1,9 @@
 #ifndef CDM_OEC_SESSION_UTIL_H_
 #define CDM_OEC_SESSION_UTIL_H_
 
-// Copyright 2016 Google Inc. All Rights Reserved.
+// Copyright 2018 Google LLC. All Rights Reserved. This file and proprietary
+// source code may only be used and distributed under the Widevine Master
+// License Agreement.
 //
 // OEMCrypto unit tests
 //
@@ -370,6 +372,9 @@ class Session {
   // The size of the encrypted message.
   size_t message_size() { return message_size_; }
 
+  // If this session has an entitlement license.
+  bool has_entitlement_license() const { return has_entitlement_license_; }
+
  private:
   // Generate mac and enc keys give the master key.
   void DeriveKeys(const uint8_t* master_key,
@@ -399,6 +404,7 @@ class Session {
   vector<uint8_t> encrypted_usage_entry_;
   uint32_t usage_entry_number_;
   string pst_;
+  bool has_entitlement_license_;
 
   // Clear Entitlement key data. This is the backing data for
   // |entitled_key_array_|.