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..abd8cc5386d40b40027abf8e3b9c4805e2fc504b 100644
--- a/ui/native_theme/native_theme.h
+++ b/ui/native_theme/native_theme.h
@@ -171,8 +171,15 @@ class NATIVE_THEME_EXPORT NativeTheme {
     int classic_state;  // Used on Windows when uxtheme is not available.
   };
 
+  enum ScrollbarOverlayColorTheme {
+    ScrollbarOverlayColorThemeDefault,
+    ScrollbarOverlayColorThemeDark,
+    ScrollbarOverlayColorThemeLight
+  };
+
   struct ScrollbarThumbExtraParams {
     bool is_hovering;
+    ScrollbarOverlayColorTheme scrollbar_theme;
   };
 
   struct SliderExtraParams {
@@ -235,7 +242,8 @@ class NATIVE_THEME_EXPORT NativeTheme {
                                     State startState,
                                     State endState,
                                     double progress,
-                                    const gfx::Rect& rect) const { }
+                                    const gfx::Rect& rect,
+                                    ScrollbarOverlayColorTheme theme) const {}
 
   // Supports theme specific colors.
   void SetScrollbarColors(unsigned inactive_color,