Use WindowTracker when resizing root window as it may delete other window in unit tests.

ash/wm/panels/panel_layout_manager.cc

Index: ash/wm/panels/panel_layout_manager.cc
diff --git a/ash/wm/panels/panel_layout_manager.cc b/ash/wm/panels/panel_layout_manager.cc
index 8e59a7fd515beee0ce7d07a2a5ed36cce5feb686..412a8d189e86315462a329f5da2a97c7d5cfcf43 100644
--- a/ash/wm/panels/panel_layout_manager.cc
+++ b/ash/wm/panels/panel_layout_manager.cc
@@ -545,9 +545,9 @@ void PanelLayoutManager::WillChangeVisibilityState(
     if (restore_windows_on_shelf_visible_) {
       scoped_ptr<aura::WindowTracker> restore_windows(
           restore_windows_on_shelf_visible_.Pass());
-      for (aura::WindowTracker::Windows::const_iterator iter =
-           restore_windows->windows().begin(); iter !=
-           restore_windows->windows().end(); ++iter) {
+      for (aura::Window::Windows::const_iterator iter =
+               restore_windows->windows().begin();
+           iter != restore_windows->windows().end(); ++iter) {
         RestorePanel(*iter);
       }
     }