Adds ability for pre-target accelerators to not consume events

ash/mus/window_manager.h

Index: ash/mus/window_manager.h
diff --git a/ash/mus/window_manager.h b/ash/mus/window_manager.h
index 1ab50466089212065f1d7b66b624024f302270c4..ab8d6ed3dee5f557a1ddae50c7e91d51536d9e87 100644
--- a/ash/mus/window_manager.h
+++ b/ash/mus/window_manager.h
@@ -100,12 +100,13 @@ class WindowManager : public ::ui::WindowManagerDelegate,
                                   bool not_responding) override;
   void OnWmNewDisplay(::ui::Window* window,
                       const display::Display& display) override;
-  void OnAccelerator(uint32_t id, const ui::Event& event) override;
   void OnWmPerformMoveLoop(::ui::Window* window,
                            ::ui::mojom::MoveLoopSource source,
                            const gfx::Point& cursor_location,
                            const base::Callback<void(bool)>& on_done) override;
   void OnWmCancelMoveLoop(::ui::Window* window) override;
+  ui::mojom::EventResult OnAccelerator(uint32_t id,
+                                       const ui::Event& event) override;
 
   shell::Connector* connector_;