Update scrollbar layer opacity when scrollbar theme changes

Source/platform/scroll/ScrollView.cpp

 /*
  * Copyright (C) 2006, 2007, 2008 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 222 matching lines @@
 IntPoint ScrollView::adjustScrollPositionWithinRange(const IntPoint& scrollPoint) const
 {
     if (!constrainsScrollingToContentEdge())
         return scrollPoint;
 
     IntPoint newScrollPosition = scrollPoint.shrunkTo(maximumScrollPosition());
     newScrollPosition = newScrollPosition.expandedTo(minimumScrollPosition());
     return newScrollPosition;
 }
 
+void ScrollView::adjustScrollbarOpacity()
+{
+    if (m_horizontalScrollbar && layerForHorizontalScrollbar()) {
+        bool isOpaqueScrollbar = !m_horizontalScrollbar->isOverlayScrollbar();
+        layerForHorizontalScrollbar()->setContentsOpaque(isOpaqueScrollbar);
+    }
+    if (m_verticalScrollbar && layerForVerticalScrollbar()) {
+        bool isOpaqueScrollbar = !m_verticalScrollbar->isOverlayScrollbar();
+        layerForVerticalScrollbar()->setContentsOpaque(isOpaqueScrollbar);
+    }
+}
+
 int ScrollView::scrollSize(ScrollbarOrientation orientation) const
 {
     Scrollbar* scrollbar = ((orientation == HorizontalScrollbar) ? m_horizontalScrollbar : m_verticalScrollbar).get();
 
     // If no scrollbars are present, the content may still be scrollable.
     if (!scrollbar) {
         IntSize scrollSize = m_contentsSize - visibleContentRect().size();
         scrollSize.clampNegativeToZero();
         return orientation == HorizontalScrollbar ? scrollSize.width() : scrollSize.height();
     }
@@ skipping 552 matching lines @@
     return cornerRect;
 }
 
 bool ScrollView::isScrollCornerVisible() const
 {
     return !scrollCornerRect().isEmpty();
 }
 
 void ScrollView::scrollbarStyleChanged()
 {
+    adjustScrollbarOpacity();
     contentsResized();
     updateScrollbars(scrollOffset());
     positionScrollbarLayers();
 }
 
 void ScrollView::updateScrollCorner()
 {
 }
 
 void ScrollView::paintScrollCorner(GraphicsContext* context, const IntRect& cornerRect)
@@ skipping 292 matching lines @@
         return;
 
     ScrollableArea::setScrollOrigin(origin);
 
     // Update if the scroll origin changes, since our position will be different if the content size did not change.
     if (updatePositionAtAll && updatePositionSynchronously)
         updateScrollbars(scrollOffset());
 }
 
 } // namespace WebCore