mash: Convert FocusCycler to wm common types and move to //ash/common

ash/aura/wm_window_aura.cc

Index: ash/aura/wm_window_aura.cc
diff --git a/ash/aura/wm_window_aura.cc b/ash/aura/wm_window_aura.cc
index e80aa71377b4ac49638db1744739d404aea25a45..741abe960795b7f531e81f345cb4ebc15cf949ef 100644
--- a/ash/aura/wm_window_aura.cc
+++ b/ash/aura/wm_window_aura.cc
@@ -517,9 +517,13 @@ void WmWindowAura::Show() {
   window_->Show();
 }
 
+views::Widget* WmWindowAura::GetInternalWidget() {
+  return views::Widget::GetWidgetForNativeView(window_);
+}
+
 void WmWindowAura::CloseWidget() {
-  DCHECK(views::Widget::GetWidgetForNativeView(window_));
-  views::Widget::GetWidgetForNativeView(window_)->Close();
+  DCHECK(GetInternalWidget());
+  GetInternalWidget()->Close();
 }
 
 bool WmWindowAura::IsFocused() const {