[New Multicolumn] Add support for column-span:all

Source/core/rendering/RenderBlockFlow.cpp

Index: Source/core/rendering/RenderBlockFlow.cpp
diff --git a/Source/core/rendering/RenderBlockFlow.cpp b/Source/core/rendering/RenderBlockFlow.cpp
index 2010d11a1b3794cccad11d30582a2c6f5bd2382e..41a661f8bf9f2c5e2001358d97a9e2919eadf212 100644
--- a/Source/core/rendering/RenderBlockFlow.cpp
+++ b/Source/core/rendering/RenderBlockFlow.cpp
@@ -1987,9 +1987,23 @@ void RenderBlockFlow::addChild(RenderObject* newChild, RenderObject* beforeChild
         flowThread->addChild(newChild, beforeChild);
         return;
     }
+    if (beforeChild) {
+        if (RenderFlowThread* containingFlowThread = flowThreadContainingBlock())
+            beforeChild = containingFlowThread->resolveMovedChild(beforeChild);
+    }
     RenderBlock::addChild(newChild, beforeChild);
 }
 
+void RenderBlockFlow::removeChild(RenderObject* oldChild)
+{
+    if (!documentBeingDestroyed()) {
+        RenderFlowThread* flowThread = multiColumnFlowThread();
+        if (flowThread && flowThread != oldChild)
+            flowThread->flowThreadRelativeWillBeRemoved(oldChild);
+    }
+    RenderBlock::removeChild(oldChild);
+}
+
 void RenderBlockFlow::moveAllChildrenIncludingFloatsTo(RenderBlock* toBlock, bool fullRemoveInsert)
 {
     RenderBlockFlow* toBlockFlow = toRenderBlockFlow(toBlock);