Add a DecryptCENC call after SelectKey for entitled sessions

Merge from Widevine repo of http://go/wvgerrit/154874

We do not require an error to come from SelectKey immediately, it can
come from a following call to DecryptCENC. This adds a function
Session::TestDecryptCENC to be called instead of SelectKey for the tests
that use entitled sessions.

Bug: 232225906
Test: tested with http://go/ag/20420224

Change-Id: If5695a5034cce371b6eb6bcf1b6467d84456c21d

libwvdrmengine/oemcrypto/test/oec_session_util.cpp

@@ -1588,6 +1588,42 @@ void Session::TestDecryptCTR(bool select_key_first,
   }
 }
 
+void Session::TestDecryptEntitled(OEMCryptoResult expected_result,
+                                  OEMCrypto_SESSION session_id,
+                                  const uint8_t* content_key_id,
+                                  size_t content_key_id_length) {
+  OEMCryptoResult select_result = OEMCrypto_SUCCESS;
+  // Select the key (from FillSimpleMessage)
+  select_result = OEMCrypto_SelectKey(
+      session_id, reinterpret_cast<const uint8_t*>(content_key_id),
+      content_key_id_length, OEMCrypto_CipherMode_CENC);
+
+  vector<uint8_t> unencrypted_data;
+  vector<uint8_t> output_buffer;
+  vector<uint8_t> encrypted_data(kTestSubsampleSectionSize);
+
+  vector<uint8_t> in_buffer(256);
+  vector<uint8_t> out_buffer(in_buffer.size());
+  OEMCrypto_SampleDescription sample_description;
+  OEMCrypto_SubSampleDescription subsample_description;
+  ASSERT_NO_FATAL_FAILURE(GenerateSimpleSampleDescription(
+      in_buffer, out_buffer, &sample_description, &subsample_description));
+  OEMCrypto_CENCEncryptPatternDesc pattern = {0, 0};
+
+  EncryptCTR(unencrypted_data, content_key_id, &sample_description.iv[0],
+             &encrypted_data);
+  // Try to decrypt the data with oemcrypto session id.
+  const OEMCryptoResult decrypt_result =
+      OEMCrypto_DecryptCENC(session_id, &sample_description, 1, &pattern);
+
+  // We only have a few errors that we test are reported.
+  ASSERT_NO_FATAL_FAILURE(
+      TestDecryptResult(expected_result, select_result, decrypt_result))
+      << "Either SelectKey or DecryptCENC should return " << expected_result
+      << ", but they returned " << select_result << " and " << decrypt_result
+      << ", respectively.";
+}
+
 void Session::TestDecryptResult(OEMCryptoResult expected_result,
                                 OEMCryptoResult actual_select_result,
                                 OEMCryptoResult actual_decrypt_result) {