Harmony - Use FocusableBorder for comboboxes on Mac

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 a9fd9829c9d8473b82c6ad70c0c9487152b9801a..2ff0120a6bcd7abd65df02afc590fcd855d9dbd1 100644
--- a/ui/views/style/platform_style.cc
+++ b/ui/views/style/platform_style.cc
@@ -58,12 +58,6 @@ std::unique_ptr<FocusableBorder> PlatformStyle::CreateComboboxBorder() {
 }
 
 // static
-std::unique_ptr<Background> PlatformStyle::CreateComboboxBackground(
-    int shoulder_width) {
-  return nullptr;
-}
-
-// static
 std::unique_ptr<ScrollBar> PlatformStyle::CreateScrollBar(bool is_horizontal) {
   return base::MakeUnique<NativeScrollBar>(is_horizontal);
 }