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 550d9b2d957931d4e1929235b8d62c5f6bd57970..b090941f43faf1c8e080b8d417e8892179e07e47 100644
--- a/ui/views/style/platform_style_mac.mm
+++ b/ui/views/style/platform_style_mac.mm
@@ -38,13 +38,36 @@ 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);
+  // When creating the background, this function always assumes the combobox is
+  // in STYLE_NORMAL. Comboboxes do not paint their backgrounds in STYLE_ACTION,
+  // so that assumption is safe.
+  return base::WrapUnique(new ComboboxBackgroundMac(
+      GetComboboxShoulderWidth(Combobox::STYLE_NORMAL)));
+}
+
+// static
+std::unique_ptr<FocusableBorder> PlatformStyle::CreateMenuButtonBorder() {
+  return base::WrapUnique(new FocusableRoundedBorder);
+}
+
+// static
+std::unique_ptr<Background> PlatformStyle::CreateMenuButtonBackground() {
+  return base::WrapUnique(
+      new ComboboxBackgroundMac(GetMenuButtonShoulderWidth()));
 }
 
 // static