Fix overlay scroll bar color on elements with dark background

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

Index: third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp b/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
index 2ac8b8d635bc885ec1edbfb9a6d7dfb028c499dd..f41e8ea4226d540579760839c8304ca3fc9a4aed 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
@@ -419,15 +419,32 @@ void ScrollableArea::setScrollbarOverlayStyle(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) {