Fix ChunkDemuxer seek deadlock

media/base/filters.h

Index: media/base/filters.h
diff --git a/media/base/filters.h b/media/base/filters.h
index 8f186d676ad8608e1cc66f4f5029c469c5e0bd5e..6379a8061117dd1b37b227bc836591ecd495ed96 100644
--- a/media/base/filters.h
+++ b/media/base/filters.h
@@ -135,7 +135,10 @@ class MEDIA_EXPORT VideoDecoder : public Filter {
   // Implementations guarantee that the callback will not be called from within
   // this method.
   //
-  // Frames will be non-NULL yet may be end of stream frames.
+  // Non-NULL frames contain decoded video data or may indicate the  end of
+  // the stream. NULL video frames indicate an aborted read. This can happen if
+  // the DemuxerStream gets flushed and doesn't have any more data to return.
+  // An aborted read indicates a seek will likely happen shortly.

[Ami GONE FROM CHROMIUM, 2012/01/27 23:44:58]

I don't like the "likely" in the last sentence here for an API contract.  Drop
the sentence or convert to something that's a specification?

(ditto for the audio version below)

[acolwell GONE FROM CHROMIUM, 2012/01/29 03:00:41]

Done.

   typedef base::Callback<void(scoped_refptr<VideoFrame>)> ReadCB;
   virtual void Read(const ReadCB& callback) = 0;
 
@@ -183,7 +186,11 @@ class MEDIA_EXPORT AudioDecoder : public Filter {
   // Implementations guarantee that the callback will not be called from within
   // this method.
   //
-  // Sample buffers will be non-NULL yet may be end of stream buffers.
+  // Non-NULL sample buffer pointers will contain decoded audio data or may
+  // indicate the end of the stream. A NULL buffer pointer indicates an aborted
+  // Read(). This can happen if the DemuxerStream gets flushed and doesn't have
+  // any more data to return. An aborted read indicates a seek will likely
+  // happen shortly.
   typedef base::Callback<void(scoped_refptr<Buffer>)> ReadCB;
   virtual void Read(const ReadCB& callback) = 0;