MenuButton: support Mac look & feel

ui/views/style/platform_style_mac.mm

Index: ui/views/style/platform_style_mac.mm
diff --git a/ui/views/style/platform_style_mac.mm b/ui/views/style/platform_style_mac.mm
index a7896442d2cdb0f3aa711e8c202432ed748804c0..09ebb9375f5366c6edbd2ea616f805efbef62b38 100644
--- a/ui/views/style/platform_style_mac.mm
+++ b/ui/views/style/platform_style_mac.mm
@@ -39,13 +39,33 @@ gfx::ImageSkia PlatformStyle::CreateComboboxArrow(bool is_enabled,
 }
 
 // static
+gfx::ImageSkia PlatformStyle::CreateMenuButtonArrow(bool is_enabled) {
+  const int kMenuButtonArrowWidth = 13;
+  return gfx::CreateVectorIcon(gfx::VectorIconId::MENU_BUTTON_ARROW_MAC,
+                               kMenuButtonArrowWidth,
+                               is_enabled ? SK_ColorWHITE : SK_ColorBLACK);
+}
+
+// static
 std::unique_ptr<FocusableBorder> PlatformStyle::CreateComboboxBorder() {
   return base::WrapUnique(new FocusableRoundedBorder);
 }
 
 // static
-std::unique_ptr<Background> PlatformStyle::CreateComboboxBackground() {
-  return base::WrapUnique(new ComboboxBackgroundMac);
+std::unique_ptr<Background> PlatformStyle::CreateComboboxBackground(
+    int shoulder_width) {
+  return base::WrapUnique(new ComboboxBackgroundMac(shoulder_width));
+}
+
+// static
+std::unique_ptr<FocusableBorder> PlatformStyle::CreateMenuButtonBorder() {
+  return base::WrapUnique(new FocusableRoundedBorder);
+}
+
+// static
+std::unique_ptr<Background> PlatformStyle::CreateMenuButtonBackground(
+    int shoulder_width) {
+  return base::WrapUnique(new ComboboxBackgroundMac(shoulder_width));
 }
 
 // static