Support start trimming post-decoding. Use it with FFmpegDemuxer.

media/filters/opus_audio_decoder.cc

Index: media/filters/opus_audio_decoder.cc
diff --git a/media/filters/opus_audio_decoder.cc b/media/filters/opus_audio_decoder.cc
index bbdcb3f575db482967be471d56df5d80f69b3c86..27c58c6023f4bbb64a77960722b6fcc37c3cea3d 100644
--- a/media/filters/opus_audio_decoder.cc
+++ b/media/filters/opus_audio_decoder.cc
@@ -418,7 +418,8 @@ bool OpusAudioDecoder::ConfigureDecoder() {
     return false;
   }
 
-  discard_helper_.reset(new AudioDiscardHelper(config_.samples_per_second()));
+  discard_helper_.reset(
+      new AudioDiscardHelper(config_.samples_per_second(), 0));

[acolwell GONE FROM CHROMIUM, 2014/05/01 01:08:34]

Is this correct? Shouldn't the config.coding_delay() get passed in here?

[DaleCurtis, 2014/05/01 01:26:32]

Not as far as I can tell, see my previous comment :)

[acolwell GONE FROM CHROMIUM, 2014/05/01 17:44:26]

Ok. This feels real counter intuitive to me. Perhaps the parameter just needs a
different name because it seems strange that Opus has a coding delay, but we are
essentially telling the AudioDiscardHelper that it doesn't. It feels like this
parameter means something different than coding delay. It just happens to equal
the coding delay in some cases.

[DaleCurtis, 2014/05/01 19:21:27]

As mentioned this is has been renamed and documented.

   start_input_timestamp_ = kNoTimestamp();
   return true;
 }