Add video decoding methods in Decryptor and add DecryptingVideoDecoder.

media/base/video_decoder.h

 // 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.
 
 #ifndef MEDIA_BASE_VIDEO_DECODER_H_
 #define MEDIA_BASE_VIDEO_DECODER_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "media/base/pipeline_status.h"
 #include "media/base/media_export.h"
 #include "ui/gfx/size.h"
 
 namespace media {
 
 class DemuxerStream;
 class VideoFrame;
 
 class MEDIA_EXPORT VideoDecoder
     : public base::RefCountedThreadSafe<VideoDecoder> {
  public:
   // Status codes for read operations on VideoDecoder.
   enum Status {
     kOk,  // Everything went as planned.
     kDecodeError,  // Decoding error happened.
     kDecryptError  // Decrypting error happened.
   };
 
-  // Initialize a VideoDecoder with the given DemuxerStream, executing the
-  // callback upon completion.
-  // statistics_cb is used to update global pipeline statistics.
+  // Initializes a VideoDecoder with the given DemuxerStream, executing the
+  // |status_cb| upon completion.
+  // |statistics_cb| is used to update the global pipeline statistics.
+  // Note: No VideoDecoder calls should be made before |status_cb| is executed.
   virtual void Initialize(const scoped_refptr<DemuxerStream>& stream,
                           const PipelineStatusCB& status_cb,
                           const StatisticsCB& statistics_cb) = 0;
 
   // Requests a frame to be decoded. The status of the decoder and decoded frame
   // are returned via the provided callback. Only one read may be in flight at
   // any given time.
   //
   // Implementations guarantee that the callback will not be called from within
   // this method.
   //
   // If the returned status is not kOk, some error has occurred in the video
   // decoder. In this case, the returned frame should always be NULL.
   //
   // Otherwise, the video decoder is in good shape. In this case, 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.
   typedef base::Callback<void(Status, const scoped_refptr<VideoFrame>&)> ReadCB;
   virtual void Read(const ReadCB& read_cb) = 0;
 
-  // Reset decoder state, fulfilling all pending ReadCB and dropping extra
+  // Resets decoder state, fulfilling all pending ReadCB and dropping extra
   // queued decoded data. After this call, the decoder is back to an initialized
   // clean state.
+  // Note: No VideoDecoder calls should be made before |closure| is executed.
   virtual void Reset(const base::Closure& closure) = 0;
 
-  // Stop decoder and set it to an uninitialized state. Note that a VideoDecoder
-  // should/could not be re-initialized after it has been stopped.
+  // Stops decoder and sets it to an uninitialized state. Note that a
+  // VideoDecoder cannot be re-initialized after it has been stopped.
+  // Note: No VideoDecoder calls should be made before |closure| is executed.
   virtual void Stop(const base::Closure& closure) = 0;
 
   // Returns true if the output format has an alpha channel. Most formats do not
   // have alpha so the default is false. Override and return true for decoders
   // that return formats with an alpha channel.
   virtual bool HasAlpha() const;
 
  protected:
   friend class base::RefCountedThreadSafe<VideoDecoder>;
   virtual ~VideoDecoder();
   VideoDecoder();
 
   DISALLOW_COPY_AND_ASSIGN(VideoDecoder);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_VIDEO_DECODER_H_