Begin tracking why layout is invalidated

Source/core/layout/SubtreeLayoutScope.cpp

 /*
  * Copyright (C) 2013 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 37 matching lines @@
 
 #if ENABLE(ASSERT)
     for (HashSet<LayoutObject*>::iterator it = m_renderersToLayout.begin(); it != m_renderersToLayout.end(); ++it)
         (*it)->assertRendererLaidOut();
 #endif
 }
 
 void SubtreeLayoutScope::setNeedsLayout(LayoutObject* descendant)
 {
     ASSERT(descendant->isDescendantOf(&m_root));
-    descendant->setNeedsLayout(MarkContainerChain, this);
+    descendant->setNeedsLayout(LayoutInvalidationReason::Unknown, MarkContainerChain, this);

[esprehn, 2015/03/23 20:19:44]

This can happen under an n^2 layout.

[pdr., 2015/03/24 03:56:19]

I'll update SubtreeLayoutScope::setNeedsLayout() to take a reason in a followup.

 }
 
 void SubtreeLayoutScope::setChildNeedsLayout(LayoutObject* descendant)
 {
     ASSERT(descendant->isDescendantOf(&m_root));
     descendant->setChildNeedsLayout(MarkContainerChain, this);
 }
 
 void SubtreeLayoutScope::addRendererToLayout(LayoutObject* renderer)
 {
 #if ENABLE(ASSERT)
     m_renderersToLayout.add(renderer);
 #endif
 }
 
 }