Add basic handling for entitlement keys in a license.

Merge from Widevine repo of http://go/wvgerrit/41834

Key rotation is not yet supported.

The key statuses are updated from a license. The
mechanism expects content keys tro come in a license.
For entitlement licenses, the content keys come in the
init_data.

This code does not yet support the key rotation event.
(A new pssh with wrapped keys is a passed to the cdm)
The policy engine/key status mechanism needs to be
updated to handle updated from the init_data.

For now, the cdm builds a license with a key container
with the content keys and used that to call
PolicyEngine::SetLicense to setup the policy engine
and key statuses.

Bug: 64003606
Bug: 70334840

Test: In child CL
Change-Id: Ibf46a18f5321cab4ff6f1778ba30527942c8021f

libwvdrmengine/cdm/core/include/key_session.h

@@ -12,7 +12,7 @@ class KeySession {
   KeySession(metrics::CryptoMetrics* metrics) : metrics_(metrics) {}
 
  public:
-  typedef enum { kDefault, kSubLicense } KeySessionType;
+  typedef enum { kDefault, kSubLicense, kEntitlement } KeySessionType;
   virtual ~KeySession() {}
   virtual KeySessionType Type() = 0;
   virtual bool GenerateDerivedKeys(const std::string& message) = 0;
@@ -26,6 +26,8 @@ class KeySession {
                                    const std::string& provider_session_token,
                                    CdmCipherMode* cipher_mode,
                                    const std::string& srm_requirement) = 0;
+  virtual OEMCryptoResult LoadEntitledContentKeys(
+      const std::vector<CryptoKey>& keys) = 0;
   virtual OEMCryptoResult SelectKey(const std::string& key_id,
                                     CdmCipherMode cipher_mode) = 0;
   virtual OEMCryptoResult Decrypt(