Do not use assets for Ash window control button backgrounds

ash/frame/custom_frame_view_ash_unittest.cc

Index: ash/frame/custom_frame_view_ash_unittest.cc
diff --git a/ash/frame/custom_frame_view_ash_unittest.cc b/ash/frame/custom_frame_view_ash_unittest.cc
index 3d227f3877fe1f76f0034f48b47bc2220b245fb6..308b565a6e3eb99e5221815aff484aa3a2c1b9b3 100644
--- a/ash/frame/custom_frame_view_ash_unittest.cc
+++ b/ash/frame/custom_frame_view_ash_unittest.cc
@@ -4,6 +4,7 @@
 
 #include "ash/frame/custom_frame_view_ash.h"
 
+#include "ash/ash_layout_constants.h"
 #include "ash/frame/caption_buttons/frame_caption_button.h"
 #include "ash/frame/caption_buttons/frame_caption_button_container_view.h"
 #include "ash/shell.h"
@@ -128,13 +129,9 @@ TEST_F(CustomFrameViewAshTest, HeaderHeight) {
   scoped_ptr<views::Widget> widget(CreateWidget(delegate));
   widget->Show();
 
-  ui::ResourceBundle& rb = ui::ResourceBundle::GetSharedInstance();
-  gfx::ImageSkia* close_button =
-      rb.GetImageSkiaNamed(IDR_AURA_WINDOW_CONTROL_BACKGROUND_H);
-
   // The header should have enough room for the window controls. The
   // header/content separator line overlays the window controls.
-  EXPECT_EQ(close_button->height(),
+  EXPECT_EQ(GetAshLayoutSize(NON_BROWSER_CAPTION_BUTTON).height(),
             delegate->custom_frame_view()->GetHeaderView()->height());
 }