[New Multicolumn] Actual support for layout of column-span:all.

Source/core/rendering/RenderObject.cpp

Index: Source/core/rendering/RenderObject.cpp
diff --git a/Source/core/rendering/RenderObject.cpp b/Source/core/rendering/RenderObject.cpp
index aa3aa7c9990aefd910ef72a60242b5bc7960a5b2..629fbd201096f51e8066e13729e3939ad6167445 100644
--- a/Source/core/rendering/RenderObject.cpp
+++ b/Source/core/rendering/RenderObject.cpp
@@ -325,6 +325,13 @@ bool RenderObject::requiresAnonymousTableWrappers(const RenderObject* newChild)
     return false;
 }
 
+bool RenderObject::isValidColumnSpanAll() const
+{
+    ASSERT(style()->columnSpan() == ColumnSpanAll);
+    RenderFlowThread* flowThread = flowThreadContainingBlock();
+    return flowThread && flowThread->isColumnSpanner(this);
+}
+
 void RenderObject::addChild(RenderObject* newChild, RenderObject* beforeChild)
 {
     ASSERT(isAllowedToModifyRenderTreeStructure(document()));