Fixes bug in FFmpegAudioDecoder where we weren't setting the usable data size.

media/filters/ffmpeg_audio_decoder.cc

Index: media/filters/ffmpeg_audio_decoder.cc
diff --git a/media/filters/ffmpeg_audio_decoder.cc b/media/filters/ffmpeg_audio_decoder.cc
index edb7a02b5915eaf8d86ed802697a1aa3b5e965d5..422709a6b109f79c6516f7a45e2d3765e8f2ca72 100644
--- a/media/filters/ffmpeg_audio_decoder.cc
+++ b/media/filters/ffmpeg_audio_decoder.cc
@@ -108,6 +108,7 @@ void FFmpegAudioDecoder::OnDecode(Buffer* input) {
   // If we have decoded something, enqueue the result.
   if (output_buffer_size) {
     DataBuffer* result_buffer = new DataBuffer(output_buffer_size);
+    result_buffer->SetDataSize(output_buffer_size);
     uint8* data = result_buffer->GetWritableData();
     memcpy(data, output_buffer, output_buffer_size);