Invalidate CustomScrollbars on having window-inactive selector.

Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 322 matching lines @@
     }
     if (didStyleChange) {
         updateScrollbarGeometry();
         updateScrollCorner();
         positionScrollbarLayers();
     }
 }
 
 void FrameView::invalidateAllCustomScrollbarsOnActiveChanged()
 {
+    if (m_frame && !m_frame->document()->styleEngine()->usesWindowInActiveSelector())
+        return;

[rune, 2015/01/20 13:42:34]

Even if this document doesn't have a :window-inactive selector, it doesn't mean
that the child iframes may not have any. You can skip the styleChanged() on the
scrollbar children, and the recalculateCustomScrollbarStyle, but  not the
recursive call into invalidateAllCustomScrollbarsOnActiveChanged.

[MuVen, 2015/01/20 14:50:11]

Done.

+
     const ChildrenWidgetSet* viewChildren = children();
     for (const RefPtrWillBeMember<Widget>& child : *viewChildren) {
         Widget* widget = child.get();
         if (widget->isFrameView())
             toFrameView(widget)->invalidateAllCustomScrollbarsOnActiveChanged();
         else if (widget->isScrollbar() && toScrollbar(widget)->isCustomScrollbar())
             toScrollbar(widget)->styleChanged();
     }
     recalculateCustomScrollbarStyle();
 }
@@ skipping 3652 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(scrollOffsetDouble());
 }
 
 } // namespace blink