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 9027c6632dd0f0365d3ca45922c63e357c996c3c..38a9f9a6cb37261716b59fbcf1810ee90d1d9cb8 100644
--- a/ui/views/style/platform_style.cc
+++ b/ui/views/style/platform_style.cc
@@ -51,11 +51,23 @@ 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() ||
@@ -70,6 +82,12 @@ 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));
 }