Aura overlay scrollbars adjust color for dark backgrounds

third_party/WebKit/public/platform/WebThemeEngine.h

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 119 matching lines @@
 
   // Extra parameters for PartProgressBar
   struct ProgressBarExtraParams {
     bool determinate;
     int valueRectX;
     int valueRectY;
     int valueRectWidth;
     int valueRectHeight;
   };
 
+  // Extra parameters for Scrollbar, now only for overlay-scrollbar
+  enum ScrollbarOverlayColorTheme {

[bokan, 2016/10/21 16:57:14]

Create a ScrollbarOverlayColorTheme.h file and put this enum in there. Use that
here and in WebScrollbar.h

+    ScrollbarOverlayColorThemeDefault,
+    ScrollbarOverlayColorThemeDark,
+    ScrollbarOverlayColorThemeLight
+  };
+
   union ExtraParams {
     ScrollbarTrackExtraParams scrollbarTrack;
     ButtonExtraParams button;
     TextFieldExtraParams textField;
     MenuListExtraParams menuList;
     SliderExtraParams slider;
     InnerSpinButtonExtraParams innerSpin;
     ProgressBarExtraParams progressBar;
+    ScrollbarOverlayColorTheme scrollbarTheme;

[bokan, 2016/10/21 16:57:14]

Similarly to the NativeTheme::ExtraParams, this isn't a union state. In this
case, thumb probably doesn't specify extra params from Web so please add a
struct ScrollbarThumbExtraParams that has the scrollbarTheme and add
ScrollbarThumbExtraParams to the union.

   };
 
   // Gets the size of the given theme part. For variable sized items
   // like vertical scrollbar thumbs, the width will be the required width of
   // the track while the height will be the minimum height.
   virtual WebSize getSize(Part) { return WebSize(); }
 
   struct ScrollbarStyle {
     int thumbThickness;
     int scrollbarMargin;
     WebColor color;
   };
 
   // Gets the overlay scrollbar style. Used for mobile theme.
   virtual void getOverlayScrollbarStyle(ScrollbarStyle*) {}
 
   // Paint the given the given theme part.
   virtual void paint(WebCanvas*,
                      Part,
                      State,
                      const WebRect&,
                      const ExtraParams*) {}
 };
 
 }  // namespace blink
 
 #endif