Add comment to unit test for renderToAssociatedSink constraint

content/renderer/media/user_media_client_impl_unittest.cc

Index: content/renderer/media/user_media_client_impl_unittest.cc
diff --git a/content/renderer/media/user_media_client_impl_unittest.cc b/content/renderer/media/user_media_client_impl_unittest.cc
index e89bb3860627fbf9c3130eea29653e1e585fb1d3..749b9866558a3d6cfd4dfdbb07d00bec2834c704 100644
--- a/content/renderer/media/user_media_client_impl_unittest.cc
+++ b/content/renderer/media/user_media_client_impl_unittest.cc
@@ -624,6 +624,9 @@ TEST_F(UserMediaClientImplTest, RenderToAssociatedSinkConstraint) {
   used_media_impl_->DeleteRequest(ms_dispatcher_->audio_input_request_id());
 
   // If audio is requested, but no constraint, it should be true.
+  // Currently we expect it to be false due to a suspected bug in the
+  // device-matching code causing issues with some sound adapters.
+  // See crbug.com/604523
   MockConstraintFactory factory;
   blink::WebMediaConstraints audio_constraints =
       factory.CreateWebMediaConstraints();