Implement "Key Presence" step in "Encrypted Block Encounted" algorithm in EME.

media/crypto/aes_decryptor_unittest.cc

Index: media/crypto/aes_decryptor_unittest.cc
diff --git a/media/crypto/aes_decryptor_unittest.cc b/media/crypto/aes_decryptor_unittest.cc
index 7877f6e895d94a4f5cd762fb9a787ea65bcf37d6..a5ce1e110940748fe922c9156cf514e32d685f0f 100644
--- a/media/crypto/aes_decryptor_unittest.cc
+++ b/media/crypto/aes_decryptor_unittest.cc
@@ -333,6 +333,17 @@ TEST_F(AesDecryptorTest, WrongKey) {
   ASSERT_NO_FATAL_FAILURE(DecryptAndExpectToFail(encrypted_data));
 }
 
+TEST_F(AesDecryptorTest, NoKey) {
+  const WebmEncryptedData& frame = kWebmEncryptedFrames[0];
+  GenerateKeyRequest(frame.key_id, frame.key_id_size);
+
+  scoped_refptr<DecoderBuffer> encrypted_data =
+      CreateWebMEncryptedBuffer(frame.encrypted_data, frame.encrypted_data_size,
+                                frame.key_id, frame.key_id_size);
+  EXPECT_CALL(*this, BufferDecrypted(AesDecryptor::kNoKey, IsNull()));
+  decryptor_.Decrypt(encrypted_data, decrypt_cb_);
+}
+
 TEST_F(AesDecryptorTest, KeyReplacement) {
   const WebmEncryptedData& frame = kWebmEncryptedFrames[0];
   GenerateKeyRequest(frame.key_id, frame.key_id_size);