Aura overlay scrollbars adjust color for dark backgrounds

third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.cpp

 /*
  * Copyright (c) 2008, 2009, 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 322 matching lines @@
   DrawingRecorder recorder(gc, scrollbar, DisplayItem::kScrollbarThumb, rect);
 
   WebThemeEngine::State state;
   WebCanvas* canvas = gc.canvas();
   if (scrollbar.pressedPart() == ThumbPart)
     state = WebThemeEngine::StatePressed;
   else if (scrollbar.hoveredPart() == ThumbPart)
     state = WebThemeEngine::StateHover;
   else
     state = WebThemeEngine::StateNormal;
+
+  blink::WebThemeEngine::ExtraParams params;
   Platform::current()->themeEngine()->paint(
       canvas, scrollbar.orientation() == HorizontalScrollbar
                   ? WebThemeEngine::PartScrollbarHorizontalThumb
                   : WebThemeEngine::PartScrollbarVerticalThumb,
-      state, WebRect(rect), 0);
+      state, WebRect(rect), &params);

[bokan, 2016/10/21 20:11:38]

Ah, this is why you had the |else| case in GetNativeThemeExtraParams, yes? In
that case, this can remain nullptr, just add an early return in
GetNativeThemeExtraParams if WebThemeEngine::ExtraParams is nullptr

 }
 
 bool ScrollbarThemeAura::shouldRepaintAllPartsOnInvalidation() const {
   // This theme can separately handle thumb invalidation.
   return false;
 }
 
 ScrollbarPart ScrollbarThemeAura::invalidateOnThumbPositionChange(
     const ScrollbarThemeClient& scrollbar,
     float oldPosition,
@@ skipping 33 matching lines @@
   }
 
   // HorizontalScrollbar
   int squareSize = scrollbar.height();
   return IntSize(
       scrollbar.width() < 2 * squareSize ? scrollbar.width() / 2 : squareSize,
       squareSize);
 }
 
 }  // namespace blink