Add AudioStreamRegistry. Move stream counting logic

content/public/test/mock_render_process_host.h

Index: content/public/test/mock_render_process_host.h
diff --git a/content/public/test/mock_render_process_host.h b/content/public/test/mock_render_process_host.h
index e246dc7d7755276ba68bc1efe6a402b6bc782606..e20b805b57c49a2404ede2f55902a1cda1ff7d20 100644
--- a/content/public/test/mock_render_process_host.h
+++ b/content/public/test/mock_render_process_host.h
@@ -145,6 +145,10 @@ class MockRenderProcessHost : public RenderProcessHost {
     remote_interfaces_ = std::move(remote_interfaces);
   }
 
+  void SetAudioStateChangedCallback(base::Closure closure) {
+    audio_state_changed_callback_ = closure;
+  }
+
  private:
   // Stores IPC messages that would have been sent to the renderer.
   IPC::TestSink sink_;
@@ -167,6 +171,7 @@ class MockRenderProcessHost : public RenderProcessHost {
   std::unique_ptr<service_manager::InterfaceProvider> remote_interfaces_;
   std::unique_ptr<mojo::AssociatedInterfacePtr<mojom::Renderer>>
       renderer_interface_;
+  base::Closure audio_state_changed_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(MockRenderProcessHost);
 };