Don't always fully repaint on viewport resize

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 1870 matching lines @@
 
     RenderView* renderView = this->renderView();
     return layoutPending()
         || (renderView && renderView->needsLayout())
         || isSubtreeLayout();
 }
 
 void FrameView::setNeedsLayout()
 {
     if (RenderView* renderView = this->renderView())
-        renderView->setNeedsLayout();
+        renderView->setNeedsLayoutWithoutForcingFullRepaint();
 }
 
 bool FrameView::isTransparent() const
 {
     return m_isTransparent;
 }
 
 void FrameView::setTransparent(bool isTransparent)
 {
     m_isTransparent = isTransparent;
@@ skipping 1343 matching lines @@
 void FrameView::willRemoveScrollbar(Scrollbar* scrollbar, ScrollbarOrientation orientation)
 {
     ScrollableArea::willRemoveScrollbar(scrollbar, orientation);
     if (AXObjectCache* cache = axObjectCache()) {
         cache->remove(scrollbar);
         cache->handleScrollbarUpdate(this);
     }
 }
 
 } // namespace WebCore