mash: Fix mash app shelf items; encapsulate ash property setup.

ash/public/cpp/window_properties.h

Index: ash/public/cpp/window_properties.h
diff --git a/ash/public/cpp/window_properties.h b/ash/public/cpp/window_properties.h
index 018703d7e78e7447e4ccd06f14de84e77cc80ea8..36f333dbd25f8255d814c0e42806e61e3830edc5 100644
--- a/ash/public/cpp/window_properties.h
+++ b/ash/public/cpp/window_properties.h
@@ -48,6 +48,11 @@ ASH_PUBLIC_EXPORT extern const aura::WindowProperty<mojom::WindowPinType>* const
 
 // Alphabetical sort.
 
+// Registers ash window properties with the MusClient's property converter.
+// Also registers various properties for mirroring to root aura::Windows.
+// This propagates ash properties set on app aura::Windows to ash, via mojo.
+void ASH_PUBLIC_EXPORT RegisterWindowPropertiesForTransportAndMirroring();
+
 }  // namespace ash
 
 #endif  // ASH_PUBLIC_CPP_WINDOW_PROPERTIES_H_