Aura overlay scrollbars adjust color for dark backgrounds

ui/native_theme/native_theme.h

Index: ui/native_theme/native_theme.h
diff --git a/ui/native_theme/native_theme.h b/ui/native_theme/native_theme.h
index 664aa50e4ee938f6bd30422bae9cf4a66220b6de..bed09c3da939f2e5b03d7b67ba8a2ccbf7001e40 100644
--- a/ui/native_theme/native_theme.h
+++ b/ui/native_theme/native_theme.h
@@ -175,6 +175,12 @@ class NATIVE_THEME_EXPORT NativeTheme {
     bool is_hovering;
   };
 
+  enum ScrollbarOverlayStyle {
+    ScrollbarOverlayStyleDefault,
+    ScrollbarOverlayStyleDark,
+    ScrollbarOverlayStyleLight
+  };
+
   struct SliderExtraParams {
     bool vertical;
     bool in_drag;
@@ -211,6 +217,7 @@ class NATIVE_THEME_EXPORT NativeTheme {
     ScrollbarArrowExtraParams scrollbar_arrow;
     ScrollbarTrackExtraParams scrollbar_track;
     ScrollbarThumbExtraParams scrollbar_thumb;
+    ScrollbarOverlayStyle scrollbar_style;
     SliderExtraParams slider;
     TextFieldExtraParams text_field;
     TrackbarExtraParams trackbar;
@@ -235,7 +242,8 @@ class NATIVE_THEME_EXPORT NativeTheme {
                                     State startState,
                                     State endState,
                                     double progress,
-                                    const gfx::Rect& rect) const { }
+                                    const gfx::Rect& rect,
+                                    ScrollbarOverlayStyle style) const { }
 
   // Supports theme specific colors.
   void SetScrollbarColors(unsigned inactive_color,