Constrain native theme menu list arrow to the paint rect

ui/native_theme/native_theme_base.cc

Index: ui/native_theme/native_theme_base.cc
diff --git a/ui/native_theme/native_theme_base.cc b/ui/native_theme/native_theme_base.cc
index dcf742cc64d70b4a405b9db12a2463fd58888e77..878882ef54acf0365af6169b410a2de175672b72 100644
--- a/ui/native_theme/native_theme_base.cc
+++ b/ui/native_theme/native_theme_base.cc
@@ -772,10 +772,22 @@ void NativeThemeBase::PaintMenuList(
   paint.setAntiAlias(true);
   paint.setStyle(SkPaint::kFill_Style);
 
+  static const int kArrowWidth = 6;
+  static const int kArrowHeight = 6;
+
+  gfx::Rect arrow(
+    menu_list.arrow_x,
+    menu_list.arrow_y - (kArrowHeight / 2),
+    kArrowWidth,
+    kArrowHeight);
+
+  // Constrain to the paint rect.
+  arrow.Intersect(rect);
+
   SkPath path;
-  path.moveTo(menu_list.arrow_x, menu_list.arrow_y - 3);
-  path.rLineTo(6, 0);
-  path.rLineTo(-3, 6);
+  path.moveTo(arrow.x(), arrow.y());
+  path.lineTo(arrow.right(), arrow.y());
+  path.lineTo(arrow.x() + arrow.width() / 2, arrow.bottom());
   path.close();
   canvas->drawPath(path, paint);
 }