Gets mustash frames looking like that of ash

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 dfedd0786c610558ef55545500b0f672b7ecbf2a..5e5918c72e74d7d80a76dee321f32cd3eeab8dee 100644
--- a/mash/wm/non_client_frame_controller.h
+++ b/mash/wm/non_client_frame_controller.h
@@ -9,6 +9,10 @@
 #include "components/mus/public/cpp/window_observer.h"
 #include "ui/views/widget/widget_delegate.h"
 
+namespace gfx {
+class Insets;
+}
+
 namespace mojo {
 class Shell;
 }
@@ -24,6 +28,9 @@ class NonClientFrameController : public views::WidgetDelegateView,
   // NonClientFrameController deletes itself when |window| is destroyed.
   NonClientFrameController(mojo::Shell* shell, mus::Window* window);
 
+  // Returns the preferred client area insets.
+  static gfx::Insets GetPreferredClientAreaInsets();
+
  private:
   ~NonClientFrameController() override;