Draw nicer arrows when the scrollbar buttons are not square.

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/gfx/geometry/rect_f.h"
 #include "ui/native_theme/native_theme.h"
 
 namespace gfx {
 class Canvas;
 class ImageSkia;
 class Rect;
 class Size;
 }
 
 namespace ui {
@@ skipping 141 matching lines @@
                   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);
+  FRIEND_TEST_ALL_PREFIXES(NativeThemeAuraTest, ArrowForNonSquareButton);
+  FRIEND_TEST_ALL_PREFIXES(NativeThemeAuraTest, BoundingRectSquare);
+  FRIEND_TEST_ALL_PREFIXES(NativeThemeAuraTest,
+                           BoundingRectSlightlyRectangular);
+  FRIEND_TEST_ALL_PREFIXES(NativeThemeAuraTest, BoundingRectVeryRectangular);
+  FRIEND_TEST_ALL_PREFIXES(NativeThemeAuraTest,
+                           BoundingRectSnappedToWholePixels);

[Peter Kasting, 2016/06/10 01:03:23]

When there are this many FRIEND_TESTs, consider whether it would make sense to
have something like "friend class NativeThemeAuraTest", make that the base for
your tests, and give it public accessors that plumb through the relevant values
on this class to the individual testcases.

Whether this is better depends on how much of the surface area of this class
you're accessing.

[Bret, 2016/06/11 00:11:43]

Since I only need PathForArrow and BoundRectForArrow I made a friend class like
you suggested.

 
   SkPath PathForArrow(const gfx::Rect& rect, Part direction) const;
+  gfx::RectF BoundingRectForArrow(const gfx::Rect& rect) 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,
@@ skipping 18 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_