Converts mash to use Shell

ash/mus/keyboard_ui_mus.h

Index: ash/mus/keyboard_ui_mus.h
diff --git a/ash/mus/keyboard_ui_mus.h b/ash/mus/keyboard_ui_mus.h
index ea4bbda8bae7fdef7dcae14ebccbd99426f5e486..a7e55461fffc077852ad1744fce82e5d7a12b1e6 100644
--- a/ash/mus/keyboard_ui_mus.h
+++ b/ash/mus/keyboard_ui_mus.h
@@ -23,6 +23,7 @@ namespace ash {
 class KeyboardUIMus : public KeyboardUI,
                       public keyboard::mojom::KeyboardObserver {
  public:
+  // |connector| may be null in tests.
   explicit KeyboardUIMus(service_manager::Connector* connector);
   ~KeyboardUIMus() override;
 
@@ -44,6 +45,7 @@ class KeyboardUIMus : public KeyboardUI,
  private:
   bool is_enabled_;
 
+  // May be null during tests.
   keyboard::mojom::KeyboardPtr keyboard_;
   mojo::Binding<keyboard::mojom::KeyboardObserver> observer_binding_;