Fix overlay scroll bar color on elements with dark background

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

 /*
  * Copyright (c) 2010, Google Inc. All rights reserved.
  * Copyright (C) 2008, 2011 Apple 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.
@@ skipping 401 matching lines @@
     Scrollbar* hScrollbar = horizontalScrollbar();
     return hScrollbar && hScrollbar->isOverlayScrollbar();
 }
 
 void ScrollableArea::setScrollbarOverlayStyle(ScrollbarOverlayStyle overlayStyle)
 {
     m_scrollbarOverlayStyle = overlayStyle;
 
     if (Scrollbar* scrollbar = horizontalScrollbar()) {
         ScrollbarTheme::theme().updateScrollbarOverlayStyle(*scrollbar);
-        setScrollbarNeedsPaintInvalidation(HorizontalScrollbar);
+        scrollbar->setNeedsPaintInvalidation(AllParts);
     }
 
     if (Scrollbar* scrollbar = verticalScrollbar()) {
         ScrollbarTheme::theme().updateScrollbarOverlayStyle(*scrollbar);
-        setScrollbarNeedsPaintInvalidation(VerticalScrollbar);
+        scrollbar->setNeedsPaintInvalidation(AllParts);
     }
 }
 
+void ScrollableArea::recalculateScrollbarOverlayStyle(Color backgroundColor)
+{
+    ScrollbarOverlayStyle oldOverlayStyle = getScrollbarOverlayStyle();
+    ScrollbarOverlayStyle overlayStyle = ScrollbarOverlayStyleDefault;
+
+    // Reduce the background color from RGB to a lightness value
+    // and determine which scrollbar style to use based on a lightness
+    // heuristic.
+    double hue, saturation, lightness;
+    backgroundColor.getHSL(hue, saturation, lightness);
+    if (lightness <= .5)
+        overlayStyle = ScrollbarOverlayStyleLight;
+
+    if (oldOverlayStyle != overlayStyle)
+        setScrollbarOverlayStyle(overlayStyle);
+}
+
 void ScrollableArea::setScrollbarNeedsPaintInvalidation(ScrollbarOrientation orientation)
 {
     if (orientation == HorizontalScrollbar) {
         if (GraphicsLayer* graphicsLayer = layerForHorizontalScrollbar()) {
             graphicsLayer->setNeedsDisplay();
             graphicsLayer->setContentsNeedsDisplay();
         }
         m_horizontalScrollbarNeedsPaintInvalidation = true;
     } else {
         if (GraphicsLayer* graphicsLayer = layerForVerticalScrollbar()) {
@@ skipping 175 matching lines @@
         std::max(0, size.height() - horizontalScrollbarHeight));
 }
 
 DEFINE_TRACE(ScrollableArea)
 {
     visitor->trace(m_scrollAnimator);
     visitor->trace(m_programmaticScrollAnimator);
 }
 
 } // namespace blink