Fix scrollbar buttons at hidpi when enable-use-zoom-for-dsf is on.

ui/native_theme/native_theme_base.h

 // Copyright (c) 2012 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.
 
 #ifndef UI_NATIVE_THEME_NATIVE_THEME_BASE_H_
 #define UI_NATIVE_THEME_NATIVE_THEME_BASE_H_
 
 #include <memory>
 
 #include "base/compiler_specific.h"
+#include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "skia/ext/platform_canvas.h"
 #include "ui/native_theme/native_theme.h"
 
 namespace gfx {
 class Canvas;
 class ImageSkia;
 class Rect;
 class Size;
 }
@@ skipping 151 matching lines @@
   // Paints the arrow used on the scrollbar and spinner.
   void PaintArrow(SkCanvas* canvas,
                   const gfx::Rect& rect,
                   Part direction,
                   SkColor color) const;
 
   // Returns the color used to draw the arrow.
   SkColor GetArrowColor(State state) const;
 
  private:
+  FRIEND_TEST_ALL_PREFIXES(NativeThemeAuraTest, VerticalArrows);
+  FRIEND_TEST_ALL_PREFIXES(NativeThemeAuraTest, HorizontalArrows);
+
+  SkPath PathForArrow(const gfx::Rect& rect, Part direction) const;
+
   void DrawVertLine(SkCanvas* canvas,
                     int x,
                     int y1,
                     int y2,
                     const SkPaint& paint) const;
   void DrawHorizLine(SkCanvas* canvas,
                      int x1,
                      int x2,
                      int y,
                      const SkPaint& paint) const;
@@ skipping 17 matching lines @@
 
   // The length of the arrow buttons, 0 means no buttons are drawn.
   unsigned int scrollbar_button_length_;
 
   DISALLOW_COPY_AND_ASSIGN(NativeThemeBase);
 };
 
 }  // namespace ui
 
 #endif  // UI_NATIVE_THEME_NATIVE_THEME_BASE_H_