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

media/filters/ffmpeg_video_decoder.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 "media/filters/ffmpeg_video_decoder.h"
 
 #include <algorithm>
 #include <string>
 
 #include "base/bind.h"
@@ skipping 210 matching lines @@
   reset_cb_.Reset();
 }
 
 void FFmpegVideoDecoder::Stop(const base::Closure& closure) {
   if (MessageLoop::current() != message_loop_) {
     message_loop_->PostTask(FROM_HERE, base::Bind(
         &FFmpegVideoDecoder::Stop, this, closure));
     return;
   }
 
+  // Tell the ProxyDecryptor to abort any pending decryptions.

[scherkus (not reviewing), 2012/08/02 18:05:32]

we don't know this is a ProxyDecyptor

I also don't think this comment adds much so I would just get rid of it

[xhwang, 2012/08/03 20:08:10]

Done.

+  if (decryptor_)
+    decryptor_->Stop();
+
   stop_cb_ = closure;
 
   // Defer stopping if a read is pending.
   if (!read_cb_.is_null())
     return;
 
   DoStop();
 }
 
 void FFmpegVideoDecoder::DoStop() {
@@ skipping 273 matching lines @@
     av_free(codec_context_);
     codec_context_ = NULL;
   }
   if (av_frame_) {
     av_free(av_frame_);
     av_frame_ = NULL;
   }
 }
 
 }  // namespace media