Decryptors can report kNoKey to WebMediaPlayer

Add callback so that kNoKey can get passed to blink in order
to generate the HTMLMediaElement.waitingforkey event.

BUG=337975
TEST=updated tests pass

Review URL: https://codereview.chromium.org/935243002

Cr-Commit-Position: refs/heads/master@{#318787}

diff --git a/media/filters/decrypting_audio_decoder_unittest.cc b/media/filters/decrypting_audio_decoder_unittest.cc
index 49df3ce..1f8395bf 100644
--- a/media/filters/decrypting_audio_decoder_unittest.cc
+++ b/media/filters/decrypting_audio_decoder_unittest.cc

@@ -63,7 +63,9 @@
             message_loop_.message_loop_proxy(),
             base::Bind(
                 &DecryptingAudioDecoderTest::RequestDecryptorNotification,
-                base::Unretained(this)))),
+                base::Unretained(this)),
+            base::Bind(&DecryptingAudioDecoderTest::OnWaitingForDecryptionKey,
+                       base::Unretained(this)))),
         decryptor_(new StrictMock<MockDecryptor>()),
         num_decrypt_and_decode_calls_(0),
         num_frames_in_decryptor_(0),
@@ -204,6 +206,7 @@
     EXPECT_CALL(*decryptor_, DecryptAndDecodeAudio(encrypted_buffer_, _))
         .WillRepeatedly(RunCallback<1>(Decryptor::kNoKey,
                                        Decryptor::AudioFrames()));
+    EXPECT_CALL(*this, OnWaitingForDecryptionKey());
     decoder_->Decode(encrypted_buffer_,
                      base::Bind(&DecryptingAudioDecoderTest::DecodeDone,
                                 base::Unretained(this)));
@@ -252,6 +255,8 @@
 
   MOCK_METHOD1(DecryptorSet, void(bool));
 
+  MOCK_METHOD0(OnWaitingForDecryptionKey, void(void));
+
   base::MessageLoop message_loop_;
   scoped_ptr<DecryptingAudioDecoder> decoder_;
   scoped_ptr<StrictMock<MockDecryptor> > decryptor_;