Remove AudioDecoder from the Filter heirarchy.

media/base/filter_collection.cc

Index: media/base/filter_collection.cc
diff --git a/media/base/filter_collection.cc b/media/base/filter_collection.cc
index 42f42d05201bb6afaf71e8e032578a1332d3e09a..f26403ce50c1dd422bd03a0c316fea7183a18e35 100644
--- a/media/base/filter_collection.cc
+++ b/media/base/filter_collection.cc
@@ -25,8 +25,8 @@ void FilterCollection::AddVideoDecoder(VideoDecoder* filter) {
   AddFilter(VIDEO_DECODER, filter);
 }
 
-void FilterCollection::AddAudioDecoder(AudioDecoder* filter) {
-  AddFilter(AUDIO_DECODER, filter);
+void FilterCollection::AddAudioDecoder(AudioDecoder* audio_decoder) {
+  audio_decoders_.push_back(audio_decoder);
 }
 
 void FilterCollection::AddVideoRenderer(VideoRenderer* filter) {
@@ -38,11 +38,12 @@ void FilterCollection::AddAudioRenderer(AudioRenderer* filter) {
 }
 
 bool FilterCollection::IsEmpty() const {
-  return filters_.empty();
+  return filters_.empty() && audio_decoders_.empty();
 }
 
 void FilterCollection::Clear() {
   filters_.clear();
+  audio_decoders_.clear();
 }
 
 void FilterCollection::SelectVideoDecoder(
@@ -50,9 +51,13 @@ void FilterCollection::SelectVideoDecoder(
   SelectFilter<VIDEO_DECODER>(filter_out);
 }
 
-void FilterCollection::SelectAudioDecoder(
-    scoped_refptr<AudioDecoder>* filter_out) {
-  SelectFilter<AUDIO_DECODER>(filter_out);
+void FilterCollection::SelectAudioDecoder(scoped_refptr<AudioDecoder>* out) {
+  if (audio_decoders_.empty()) {
+    *out = NULL;
+    return;
+  }
+  *out = audio_decoders_.front();
+  audio_decoders_.pop_front();
 }
 
 void FilterCollection::SelectVideoRenderer(