Use nine-patch resource for drawing Aura overlay scrollbar thumb.

cc/trees/layer_tree_host_pixeltest_scrollbars.cc

 // Copyright 2016 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 <stddef.h>
 
 #include "base/memory/ptr_util.h"
 #include "build/build_config.h"
 #include "cc/input/scrollbar.h"
 #include "cc/layers/painted_scrollbar_layer.h"
@@ skipping 49 matching lines @@
 
     gfx::Rect inset_rect = content_rect;
     while (!inset_rect.IsEmpty()) {
       int big = paint_scale_ + 2;
       int small = paint_scale_;
       inset_rect.Inset(big, big, small, small);
       canvas->drawRect(RectToSkRect(inset_rect), flags);
       inset_rect.Inset(big, big, small, small);
     }
   }
+  bool UsesNinePatchThumbResource() const override { return false; }
+  gfx::Size NinePatchThumbCanvasSize() const override { return gfx::Size(); }
+  gfx::Rect NinePatchThumbAperture() const override { return gfx::Rect(); }
 
   void set_paint_scale(int scale) { paint_scale_ = scale; }
 
  private:
   int paint_scale_ = 4;
   bool thumb_ = false;
   SkColor color_ = SK_ColorGREEN;
   gfx::Rect rect_;
 };
 
@@ skipping 85 matching lines @@
   layer->SetTransform(scale_transform);
 
   RunPixelTest(PIXEL_TEST_GL, background,
                base::FilePath(FILE_PATH_LITERAL("spiral_64_scale.png")));
 }
 
 }  // namespace
 }  // namespace cc
 
 #endif  // OS_ANDROID