Revert of Remove AudioBuffer::set_duration(), instead base on frames.

media/base/audio_discard_helper.cc

 // Copyright 2014 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/base/audio_discard_helper.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "media/base/audio_buffer.h"
@@ skipping 85 matching lines @@
 
     // If everything would be discarded, indicate a new buffer is required.
     if (end_frames_to_discard == decoded_frames)
       return false;
 
     decoded_buffer->TrimEnd(end_frames_to_discard);
   } else {
     DCHECK(encoded_buffer->discard_padding() == base::TimeDelta());
   }
 
-  // Assign timestamp to the buffer.
+  // Assign timestamp and duration to the buffer.
   decoded_buffer->set_timestamp(timestamp_helper_.GetTimestamp());
+  decoded_buffer->set_duration(
+      timestamp_helper_.GetFrameDuration(decoded_buffer->frame_count()));
   timestamp_helper_.AddFrames(decoded_buffer->frame_count());
   return true;
 }
 
 }  // namespace media