Do not change video decoder collection unless it is indeed a media stream.

webkit/media/filter_helpers.cc

Index: webkit/media/filter_helpers.cc
===================================================================
--- webkit/media/filter_helpers.cc	(revision 126489)
+++ webkit/media/filter_helpers.cc	(working copy)
@@ -38,6 +38,11 @@
   if (!client)

[Ami GONE FROM CHROMIUM, 2012/03/14 22:00:09]

I thought this was what prevented non-mediastreams from clearing decoders.
In what scenario is client!=NULL but client->GetVideoDecoder()==NULL ?

     return false;
 
+  scoped_refptr<media::VideoDecoder> video_decoder = client->GetVideoDecoder(
+      url, message_loop_factory);
+  if (!video_decoder)
+    return false;
+
   // Remove any "traditional" decoders (e.g. GpuVideoDecoder) from the
   // collection.
   // NOTE: http://crbug.com/110800 is about replacing this ad-hockery with
@@ -47,11 +52,6 @@
     filter_collection->SelectVideoDecoder(&old_videodecoder);
   } while (old_videodecoder);
 
-  scoped_refptr<media::VideoDecoder> video_decoder = client->GetVideoDecoder(
-      url, message_loop_factory);
-  if (!video_decoder)
-    return false;
-
   filter_collection->AddVideoDecoder(video_decoder);
 
   // TODO(vrk/wjia): Setting true for local_source is under the assumption