Aura overlay scrollbars adjust color for dark backgrounds

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 b991948fc11d2ae8bbdbd734b007b4528396ef94..82d8a42b3ec5f29facf8f62a97151616e615a0d8 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
@@ -403,17 +403,27 @@ void ScrollableArea::setScrollbarOverlayStyle(
   }
 }
 
-void ScrollableArea::recalculateScrollbarOverlayStyle(Color backgroundColor) {
-  ScrollbarOverlayStyle oldOverlayStyle = getScrollbarOverlayStyle();
-  ScrollbarOverlayStyle overlayStyle = ScrollbarOverlayStyleDefault;
-
+ScrollbarOverlayStyle ScrollableArea::calculateScrollbarOverlayStyle(
+    Color backgroundColor) {
   // 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;
+    return ScrollbarOverlayStyleLight;
+  return ScrollbarOverlayStyleDark;
+}
+
+void ScrollableArea::recalculateScrollbarOverlayStyle(Color backgroundColor,
+                                                      bool isTransparent) {
+  ScrollbarOverlayStyle oldOverlayStyle = getScrollbarOverlayStyle();
+  ScrollbarOverlayStyle overlayStyle = ScrollbarOverlayStyleDefault;
+
+  // will calc color when paint if it is transparent
+  if (!isTransparent) {
+    overlayStyle = calculateScrollbarOverlayStyle(backgroundColor);
+  }
 
   if (oldOverlayStyle != overlayStyle)
     setScrollbarOverlayStyle(overlayStyle);