Add support for partial append window end trimming.

media/base/audio_discard_helper.h

Index: media/base/audio_discard_helper.h
diff --git a/media/base/audio_discard_helper.h b/media/base/audio_discard_helper.h
index deeb45f37ea8eef4600f0142bfbe7ec1eef0ba3f..2c020366543a5adfb5fa118a9b90cab9a8aa661e 100644
--- a/media/base/audio_discard_helper.h
+++ b/media/base/audio_discard_helper.h
@@ -31,8 +31,6 @@ class MEDIA_EXPORT AudioDiscardHelper {
   // corresponding to the first encoded buffer is output.  These frames are not
   // represented in the encoded data stream and instead are an artifact of how
   // most MP3 decoders work.  See http://lame.sourceforge.net/tech-FAQ.txt
-  //
-  // NOTE: End discard is only supported when there is no |decoder_delay|.
   AudioDiscardHelper(int sample_rate, size_t decoder_delay);
   ~AudioDiscardHelper();
 
@@ -73,6 +71,11 @@ class MEDIA_EXPORT AudioDiscardHelper {
   bool delayed_discard_;
   DecoderBuffer::DiscardPadding delayed_discard_padding_;
 
+  // When |decoder_delay_| > 0, the number of frames which should be discarded
+  // from the next buffer.  The index at which to start discarding is calculated
+  // by subtracting |delayed_end_discard_| from |decoder_delay_|.
+  size_t delayed_end_discard_;
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(AudioDiscardHelper);
 };