Don't always fully repaint on viewport resize

Source/core/rendering/style/FillLayer.cpp

 /*
  * Copyright (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 337 matching lines @@
 {
     const FillLayer* curr;
     for (curr = this; curr; curr = curr->next()) {
         if (curr->m_image && !curr->m_image->isLoaded())
             return false;
     }
 
     return true;
 }
 
+bool FillLayer::needsFullRepaintOnContainerWidthChange() const
+{
+    if (m_image) {
+        if (m_repeatX != RepeatFill && m_repeatX != NoRepeatFill)
+            return true;
+        if (m_xPosition.isPercent() && !m_xPosition.isZero())
+            return true;
+        if (m_backgroundXOrigin != LeftEdge)
+            return true;
+        if (m_sizeType != SizeLength && m_sizeType != SizeNone)
+            return true;
+        if (m_sizeType == SizeLength) {
+            if (m_sizeLength.width().isPercent() && !m_sizeLength.width().isZero())
+                return true;
+            if (m_sizeLength.width().isAuto() && m_sizeLength.height().isPercent() && !m_sizeLength.height().isZero())
+                return true;
+        }
+    }
+
+    return m_next && m_next->needsFullRepaintOnContainerWidthChange();
+}
+
+bool FillLayer::needsFullRepaintOnContainerHeightChange() const
+{
+    if (m_image) {
+        if (m_repeatY != RepeatFill && m_repeatY != NoRepeatFill)
+            return true;
+        if (m_yPosition.isPercent() && !m_yPosition.isZero())
+            return true;
+        if (m_backgroundYOrigin != TopEdge)
+            return true;
+        if (m_sizeType != SizeLength && m_sizeType != SizeNone)
+            return true;
+        if (m_sizeType == SizeLength) {
+            if (m_sizeLength.height().isPercent() && !m_sizeLength.height().isZero())
+                return true;
+            if (m_sizeLength.height().isAuto() && m_sizeLength.width().isPercent() && !m_sizeLength.width().isZero())
+                return true;
+        }
+    }
+
+    return m_next && m_next->needsFullRepaintOnContainerHeightChange();
+}
+
 bool FillLayer::hasOpaqueImage(const RenderObject* renderer) const
 {
     if (!m_image)
         return false;
 
     if (m_composite == CompositeClear || m_composite == CompositeCopy)
         return true;
 
     if (m_blendMode != blink::WebBlendModeNormal)
         return false;
 
     if (m_composite == CompositeSourceOver)
         return m_image->knownToBeOpaque(renderer);
 
     return false;
 }
 
 bool FillLayer::hasRepeatXY() const
 {
     return m_repeatX == RepeatFill && m_repeatY == RepeatFill;
 }
 
 } // namespace WebCore