CompositingReasonFinder should use a virtual function instead of a nest of branches

Source/core/rendering/RenderObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 2766 matching lines @@
     }
     for (RenderObject* curr = firstChild(); curr; curr = curr->nextSibling())
         curr->updateDragState(dragOn);
 }
 
 CompositingState RenderObject::compositingState() const
 {
     return hasLayer() ? toRenderLayerModelObject(this)->layer()->compositingState() : NotComposited;
 }
 
+CompositingReasons RenderObject::additionalCompositingReasons(CompositingTriggerFlags) const
+{
+    return CompositingReasonNone;
+}
+
 bool RenderObject::acceleratedCompositingForOverflowScrollEnabled() const
 {
     const Settings* settings = document().settings();
     return settings && settings->acceleratedCompositingForOverflowScrollEnabled();
 }
 
 // FIXME: This is a temporary flag and should be removed once accelerated
 // overflow scroll is ready (crbug.com/254111).
 bool RenderObject::compositorDrivenAcceleratedScrollingEnabled() const
 {
@@ skipping 555 matching lines @@
 {
     if (object1) {
         const WebCore::RenderObject* root = object1;
         while (root->parent())
             root = root->parent();
         root->showRenderTreeAndMark(object1, "*", object2, "-", 0);
     }
 }
 
 #endif