Move Pipeline permanent callbacks into Pipeline::Client interface.

media/base/pipeline_client.h

+// Copyright 2016 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_PIPELINE_CLIENT_H_
+#define MEDIA_BASE_PIPELINE_CLIENT_H_
+
+#include "media/base/buffering_state.h"
+#include "media/base/pipeline_metadata.h"
+#include "media/base/pipeline_status.h"
+#include "media/base/text_track.h"
+
+namespace media {
+
+class PipelineClient {

[xhwang, 2016/04/21 05:50:35]

This can also be a inner class, e.g. Pipeline::Client, which IMHO is cleaner
since the interface and client interface will be in the same file. We have a
similar model for the mojo interface and mojo client interface.

[alokp, 2016/04/21 21:56:38]

Sure. Do you have a better name for Client? Now that we are passing it at Start,
I do think this is a good name anymore, may be Pipeline::PlaybackCallbacks?

+ public:
+  virtual ~PipelineClient() {}
+
+  // Executed whenever an error occurs but hasn't been reported already through
+  // another callback.
+  virtual void OnError(PipelineStatus status) {}
+
+  // Executed whenever the media reaches the end.
+  virtual void OnEnded() {}
+
+  // Executed when the content duration, container video size, start time, and
+  // whether the content has audio and/or video in supported formats are known.
+  virtual void OnMetadata(PipelineMetadata metadata) {}
+
+  // Executed whenever there are changes in the buffering state of the pipeline.
+  virtual void OnBufferingStateChange(BufferingState state) {}
+
+  // Executed whenever the presentation duration changes.
+  virtual void OnDurationChange() {}
+
+  // Executed whenever a text track is added.
+  virtual void OnAddTextTrack(const TextTrackConfig& config,
+                              const AddTextTrackDoneCB& done_cb) {}
+
+  // Executed whenever the key needed to decrypt the stream is not available.
+  virtual void OnWaitingForDecryptionKey() {}
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_PIPELINE_CLIENT_H_