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

webkit/media/crypto/ppapi_decryptor.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "webkit/media/crypto/ppapi_decryptor.h"
 
 #include "base/logging.h"
 #include "media/base/decoder_buffer.h"
 #include "media/base/decryptor_client.h"
 #include "webkit/media/crypto/key_systems.h"
@@ skipping 49 matching lines @@
     const DecryptCB& decrypt_cb) {
   DCHECK(cdm_plugin_);
   // TODO(xhwang): Enable the following once we have updated PluginInstance.
   // TODO(xhwang): Need to figure out thread safety about PPP calls.
   // if (!cdm_plugin_->Decrypt(
   //     encrypted, base::Bind(&PpapiDecryptor::DataReady, this, decrypt_cb))) {
   //   decrypt_cb.Run(kError, NULL);
   // }
 }
 
+void PpapiDecryptor::Stop() {
+}
+
 void PpapiDecryptor::DataReady(const DecryptCB& decrypt_cb,
                                const uint8* data, int data_size ) {
   DCHECK(!decrypt_cb.is_null());
   scoped_refptr<media::DecoderBuffer> decrypted_data =
       media::DecoderBuffer::CopyFrom(data, data_size);
   decrypt_cb.Run(kSuccess, decrypted_data);
 }
 
 }  // namespace webkit_media