mash shelf: Don't create shelf DimmerView in ShelfWidget on mus

ash/aura/wm_shelf_aura.cc

Index: ash/aura/wm_shelf_aura.cc
diff --git a/ash/aura/wm_shelf_aura.cc b/ash/aura/wm_shelf_aura.cc
index 9d6274c0e07c65f423f2e30beac8d8841a0d1e8b..25e60bb97e701f4870688b49844fa1b4b872f018 100644
--- a/ash/aura/wm_shelf_aura.cc
+++ b/ash/aura/wm_shelf_aura.cc
@@ -7,6 +7,7 @@
 #include "ash/aura/wm_window_aura.h"
 #include "ash/common/shelf/wm_shelf_observer.h"
 #include "ash/common/wm_window.h"
+#include "ash/shelf/dimmer_view.h"
 #include "ash/shelf/shelf.h"
 #include "ash/shelf/shelf_layout_manager.h"
 #include "ash/shell.h"
@@ -120,6 +121,10 @@ ShelfBackgroundType WmShelfAura::GetBackgroundType() const {
   return shelf_layout_manager_->shelf_widget()->GetBackgroundType();
 }
 
+WmDimmerView* WmShelfAura::CreateDimmerView(bool disable_animations_for_test) {
+  return DimmerView::Create(this, disable_animations_for_test);
+}
+
 bool WmShelfAura::IsDimmed() const {
   return shelf_layout_manager_->shelf_widget()->GetDimsShelf();
 }