Extract shell methods from ApplicationImpl into a base class, and pass this to Initialize() instead.

mash/wm/non_client_frame_controller.h

Index: mash/wm/non_client_frame_controller.h
diff --git a/mash/wm/non_client_frame_controller.h b/mash/wm/non_client_frame_controller.h
index dfb7b4fd0f9014a438ef2a368fe23f6a376c4420..b5346f25e5e599ed964f6aad778a27836137273f 100644
--- a/mash/wm/non_client_frame_controller.h
+++ b/mash/wm/non_client_frame_controller.h
@@ -17,12 +17,8 @@ class Insets;
 }
 
 namespace mojo {
-namespace shell {
-namespace mojom {
 class Shell;
 }
-}
-}
 
 namespace mus {
 class Window;
@@ -37,7 +33,7 @@ class NonClientFrameController : public views::WidgetDelegateView,
                                  public mus::WindowObserver {
  public:
   // NonClientFrameController deletes itself when |window| is destroyed.
-  NonClientFrameController(mojo::shell::mojom::Shell* shell,
+  NonClientFrameController(mojo::Shell* shell,
                            mus::Window* window,
                            mus::WindowManagerClient* window_manager_client);