Invalidate only non-scrolling layers for non-scrolling content.

third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google 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
@@ skipping 417 matching lines @@
 
     // FIXME: generalize accessors to backing GraphicsLayers so that this code is squashing-agnostic.
     if (layer()->groupedMapping()) {
         LayoutRect paintInvalidationRect = r;
         if (GraphicsLayer* squashingLayer = layer()->groupedMapping()->squashingLayer()) {
             // Note: the subpixel accumulation of layer() does not need to be added here. It is already taken into account.
             squashingLayer->setNeedsDisplayInRect(enclosingIntRect(paintInvalidationRect), invalidationReason, object);
         }
     } else if (compositedScrollsWithRespectTo(&object, *this)) {
         layer()->compositedLayerMapping()->setScrollingContentsNeedDisplayInRect(r, invalidationReason, object);
+    } else if (usesCompositedScrolling()) {
+        layer()->compositedLayerMapping()->setNonScrollingContentsNeedDisplayInRect(r, invalidationReason, object);
     } else {
-        // TODO(chrishtr): we should be able to skip scrolling content layers in this case.
+        // Otherwise invalidate everything.
         layer()->compositedLayerMapping()->setContentsNeedDisplayInRect(r, invalidationReason, object);
     }
 }
 
 void LayoutBoxModelObject::invalidateDisplayItemClientOnBacking(const DisplayItemClient& displayItemClient, PaintInvalidationReason invalidationReason, const LayoutObject* layoutObject) const
 {
     displayItemClient.setDisplayItemsUncached();
 
     // We need to inform the GraphicsLayer about this paint invalidation only when we are tracking
     // paint invalidation or ENABLE(ASSERT).
@@ skipping 679 matching lines @@
     if (rootElementStyle->hasBackground())
         return false;
 
     if (node() != document().firstBodyElement())
         return false;
 
     return true;
 }
 
 } // namespace blink