Fix invalidation during painting of scrollbars

Source/platform/scroll/Scrollbar.cpp

 /*
  * Copyright (C) 2004, 2006, 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 87 matching lines @@
         return;
 
     ASSERT(m_scrollableArea);
     if (m_orientation == VerticalScrollbar)
         m_animator->willRemoveVerticalScrollbar(this);
     else
         m_animator->willRemoveHorizontalScrollbar(this);
 #endif
 }
 
+void Scrollbar::setFrameRect(const IntRect& frameRect)
+{
+    if (frameRect == this->frameRect())
+        return;
+
+    invalidate();
+    Widget::setFrameRect(frameRect);
+    invalidate();
+}
+
 ScrollbarOverlayStyle Scrollbar::scrollbarOverlayStyle() const
 {
     return m_scrollableArea ? m_scrollableArea->scrollbarOverlayStyle() : ScrollbarOverlayStyleDefault;
 }
 
 void Scrollbar::getTickmarks(Vector<IntRect>& tickmarks) const
 {
     if (m_scrollableArea)
         m_scrollableArea->getTickmarks(tickmarks);
 }
@@ skipping 437 matching lines @@
 
     return m_scrollableArea->scrollPosition().y() - m_scrollableArea->minimumScrollPosition().y();
 }
 
 DisplayItemClient Scrollbar::displayItemClient() const
 {
     return m_scrollableArea->displayItemClient();
 }
 
 } // namespace blink