Support additional mash shelf alignments.

mash/wm/root_window_controller.h

Index: mash/wm/root_window_controller.h
diff --git a/mash/wm/root_window_controller.h b/mash/wm/root_window_controller.h
index d3f3142112ef315392d349520ee6e39e6e9ec329..8e7471ae2068bc9c6d10f00a0ac85718f0e5de86 100644
--- a/mash/wm/root_window_controller.h
+++ b/mash/wm/root_window_controller.h
@@ -31,6 +31,7 @@ namespace wm {
 
 class LayoutManager;
 class ShadowController;
+class ShelfLayout;
 class WindowManager;
 class WindowManagerApplication;
 
@@ -65,6 +66,8 @@ class RootWindowController : public mus::WindowObserver,
 
   void OnAccelerator(uint32_t id, const ui::Event& event);
 
+  ShelfLayout* GetShelfLayoutManager();
+
  private:
   explicit RootWindowController(WindowManagerApplication* app);
   ~RootWindowController() override;