wrench_menu: use NativeTheme colors under aura

ui/native_theme/native_theme_gtk.cc

Index: ui/native_theme/native_theme_gtk.cc
diff --git a/ui/native_theme/native_theme_gtk.cc b/ui/native_theme/native_theme_gtk.cc
index 07209d8594b4d13cef3626f7b68a5569a1988c1e..cc8a4d87bc66ba642f65b540f7a5ee81d7f263b1 100644
--- a/ui/native_theme/native_theme_gtk.cc
+++ b/ui/native_theme/native_theme_gtk.cc
@@ -20,6 +20,9 @@ const SkColor kInvalidColorIdColor = SkColorSetRGB(255, 0, 128);
 const SkColor kFocusedBorderColor = SkColorSetRGB(0x4D, 0x90, 0xFE);
 const SkColor kUnfocusedBorderColor = SkColorSetRGB(0xD9, 0xD9, 0xD9);
 
+// MenuItem
+const SkColor kHoverMenuItemBackgroundColor = SkColorSetRGB(204, 204, 204);
+
 // TextButton:
 const SkColor kTextButtonBackgroundColor = SkColorSetRGB(0xde, 0xde, 0xde);
 const SkColor kTextButtonEnabledColor = SkColorSetRGB(6, 45, 117);
@@ -59,6 +62,10 @@ SkColor NativeThemeGtk::GetSystemColor(ColorId color_id) const {
     case kColorId_UnfocusedBorderColor:
       return kUnfocusedBorderColor;
 
+    // MenuItem
+    case kColorId_HoverMenuItemBackgroundColor:
+      return kHoverMenuItemBackgroundColor;
+
     // TextButton:
     case kColorId_TextButtonBackgroundColor:
       return kTextButtonBackgroundColor;