Enable ash window cycle UI by default.

ash/wm/window_mirror_view.cc

Index: ash/wm/window_mirror_view.cc
diff --git a/ash/wm/window_mirror_view.cc b/ash/wm/window_mirror_view.cc
index 58c89e1a705f55265d8db2f502798b82983c7b04..374207c1c61cc35bec7ca4d259119404fcc4ffd2 100644
--- a/ash/wm/window_mirror_view.cc
+++ b/ash/wm/window_mirror_view.cc
@@ -104,6 +104,9 @@ ui::Layer* WindowMirrorView::GetMirrorLayer() {
 }
 
 gfx::Rect WindowMirrorView::GetClientAreaBounds() const {
+  // The target window may not have a widget in unit tests.
+  if (!target_->GetInternalWidget())
+    return gfx::Rect();
   views::View* client_view = target_->GetInternalWidget()->client_view();
   return client_view->ConvertRectToWidget(client_view->GetLocalBounds());
 }