Do not use assets for Ash window control button backgrounds

ash/frame/caption_buttons/frame_size_button_unittest.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/frame/caption_buttons/frame_size_button.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"
 #include "ash/test/ash_test_base.h"
@@ skipping 39 matching lines @@
     caption_button_container_->SetBounds(width() - preferred_size.width(), 0,
         preferred_size.width(), preferred_size.height());
   }
 
   void ViewHierarchyChanged(
       const ViewHierarchyChangedDetails& details) override {
     if (details.is_add && details.child == this) {
       caption_button_container_ =
           new FrameCaptionButtonContainerView(GetWidget());
 
-      // Set arbitrary images for the container's buttons so that the buttons
-      // have non-empty sizes.
+      // Set arbitrary images for the button icons and assign a non-empty size.
+      caption_button_container_->SetButtonSize(gfx::Size(32, 33));
       for (int icon = 0; icon < CAPTION_BUTTON_ICON_COUNT; ++icon) {
-        caption_button_container_->SetButtonImages(
+        caption_button_container_->SetButtonImage(
             static_cast<CaptionButtonIcon>(icon),
-            IDR_AURA_WINDOW_CONTROL_ICON_CLOSE,
-            IDR_AURA_WINDOW_CONTROL_BACKGROUND_H,
-            IDR_AURA_WINDOW_CONTROL_BACKGROUND_P);
+            IDR_AURA_WINDOW_CONTROL_ICON_CLOSE);
       }
 
       AddChildView(caption_button_container_);
     }
   }
 
   // Not owned.
   ash::FrameCaptionButtonContainerView* caption_button_container_;
 
   DISALLOW_COPY_AND_ASSIGN(TestWidgetDelegate);
@@ skipping 380 matching lines @@
 
   // None of the buttons should stay pressed and the buttons should have their
   // regular icons.
   EXPECT_TRUE(AllButtonsInNormalState());
   EXPECT_EQ(CAPTION_BUTTON_ICON_MINIMIZE, minimize_button()->icon());
   EXPECT_EQ(CAPTION_BUTTON_ICON_CLOSE, close_button()->icon());
 }
 
 }  // namespace test
 }  // namespace ash