Add IPCs for ash display shortcuts.

ash/mus/accelerators/accelerator_controller_delegate_mus.h

Index: ash/mus/accelerators/accelerator_controller_delegate_mus.h
diff --git a/ash/mus/accelerators/accelerator_controller_delegate_mus.h b/ash/mus/accelerators/accelerator_controller_delegate_mus.h
index 4d14750ea97ceb16fb0f9cc2d9ab59f945e7b562..79a30fee2c6c59293db9aa779dd01a0266e368de 100644
--- a/ash/mus/accelerators/accelerator_controller_delegate_mus.h
+++ b/ash/mus/accelerators/accelerator_controller_delegate_mus.h
@@ -13,6 +13,7 @@ namespace mus {
 
 class WindowManager;
 
+// Controls accelerators that are specific to mash.
 class AcceleratorControllerDelegateMus : public AcceleratorControllerDelegate {
  public:
   explicit AcceleratorControllerDelegateMus(WindowManager* window_manager);