MenuButton: support Mac look & feel

ui/views/style/platform_style.cc

Index: ui/views/style/platform_style.cc
diff --git a/ui/views/style/platform_style.cc b/ui/views/style/platform_style.cc
index a303d84cd760ce78040ed17287e711afcce4fa6e..cf30231649b19eaa7ddffb1a9847722ae6ab8ac7 100644
--- a/ui/views/style/platform_style.cc
+++ b/ui/views/style/platform_style.cc
@@ -52,11 +52,23 @@ std::unique_ptr<FocusableBorder> PlatformStyle::CreateComboboxBorder() {
 }
 
 // static
-std::unique_ptr<Background> PlatformStyle::CreateComboboxBackground() {
+std::unique_ptr<Background> PlatformStyle::CreateComboboxBackground(
+    int shoulder_width) {
   return nullptr;
 }
 
 // static
+std::unique_ptr<Background> PlatformStyle::CreateMenuButtonBackground(
+    int shoulder_width) {
+  return nullptr;
+}
+
+// static
+std::unique_ptr<FocusableBorder> PlatformStyle::CreateMenuButtonBorder() {
+  return base::WrapUnique(new FocusableBorder());
+}
+
+// static
 std::unique_ptr<LabelButtonBorder> PlatformStyle::CreateLabelButtonBorder(
     Button::ButtonStyle style) {
   if (!ui::MaterialDesignController::IsModeMaterial() ||
@@ -71,6 +83,12 @@ std::unique_ptr<LabelButtonBorder> PlatformStyle::CreateLabelButtonBorder(
 }
 
 // static
+gfx::ImageSkia PlatformStyle::CreateMenuButtonArrow(bool is_enabled) {
+  ui::ResourceBundle& rb = ui::ResourceBundle::GetSharedInstance();
+  return *rb.GetImageSkiaNamed(IDR_MENU_DROPARROW);
+}
+
+// static
 std::unique_ptr<ScrollBar> PlatformStyle::CreateScrollBar(bool is_horizontal) {
   return base::WrapUnique(new NativeScrollBar(is_horizontal));
 }