Begin tracking why layout is invalidated

Source/core/layout/SubtreeLayoutScope.cpp

Index: Source/core/layout/SubtreeLayoutScope.cpp
diff --git a/Source/core/layout/SubtreeLayoutScope.cpp b/Source/core/layout/SubtreeLayoutScope.cpp
index 2a529e28497bb51e5cc533638d85f368cc4a3ddb..46c4caab770c9542c9bb9cb3cbd99c48710ac9d7 100644
--- a/Source/core/layout/SubtreeLayoutScope.cpp
+++ b/Source/core/layout/SubtreeLayoutScope.cpp
@@ -55,7 +55,7 @@ SubtreeLayoutScope::~SubtreeLayoutScope()
 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)