Use NativeTheme to draw vertical menu separators.

chrome/browser/ui/libgtkui/native_theme_gtk2.cc

Index: chrome/browser/ui/libgtkui/native_theme_gtk2.cc
diff --git a/chrome/browser/ui/libgtkui/native_theme_gtk2.cc b/chrome/browser/ui/libgtkui/native_theme_gtk2.cc
index c1a16219c9c59e791f5e2faee99f64851d59bb5a..af67e8343f5af8cb1e01c93989650107309efb89 100644
--- a/chrome/browser/ui/libgtkui/native_theme_gtk2.cc
+++ b/chrome/browser/ui/libgtkui/native_theme_gtk2.cc
@@ -156,15 +156,9 @@ SkColor NativeThemeGtk2::GetSystemColor(ColorId color_id) const {
     case kColorId_MenuItemSubtitleColor:
     case kColorId_DisabledMenuItemForegroundColor:
       return GetTextColor(GetMenuItem(), INSENSITIVE);
-    case kColorId_FocusedMenuButtonBorderColor:
-      return GetBgColor(GetEntry(), NORMAL);
-    case kColorId_HoverMenuButtonBorderColor:
-      return GetTextAAColor(GetEntry(), PRELIGHT);
     case kColorId_MenuBorderColor:
-    case kColorId_EnabledMenuButtonBorderColor:
-    case kColorId_MenuSeparatorColor: {
+    case kColorId_MenuSeparatorColor:
       return GetTextColor(GetMenuItem(), INSENSITIVE);
-    }
     case kColorId_MenuBackgroundColor:
       return GetBgColor(GetMenu(), NORMAL);