Draw nicer arrows when the scrollbar buttons are not square.

ui/native_theme/native_theme_base.h

Index: ui/native_theme/native_theme_base.h
diff --git a/ui/native_theme/native_theme_base.h b/ui/native_theme/native_theme_base.h
index 74525ce67fbf4dfcbbc7d2cc3356ae6d797178e2..e92b21d21d1cf94e8e1fee8837615b3957cfc537 100644
--- a/ui/native_theme/native_theme_base.h
+++ b/ui/native_theme/native_theme_base.h
@@ -11,6 +11,7 @@
 #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 {
@@ -172,8 +173,16 @@ class NATIVE_THEME_EXPORT NativeThemeBase : public NativeTheme {
  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,