Don't delete a flow thread just because it becomes childless.

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 ade24833002626b55b6ec9a6bf42e23f145039b4..5eb48e079a166492c8091ab6348428fec15d1324 100644
--- a/Source/core/rendering/RenderObject.cpp
+++ b/Source/core/rendering/RenderObject.cpp
@@ -2400,8 +2400,9 @@ void RenderObject::destroyAndCleanupAnonymousWrappers()
         // Anonymous block continuations are tracked and destroyed elsewhere (see the bottom of RenderBlock::removeChild)
         if (destroyRootParent->isRenderBlock() && toRenderBlock(destroyRootParent)->isAnonymousBlockContinuation())
             break;
-        // Column spans are tracked elsewhere, so we can't destroy them here.
-        if (destroyRootParent->isAnonymousColumnSpanBlock())
+        // A flow thread is tracked by its containing block. Whether its children are removed or not is irrelevant.
+        // Column spans are tracked elsewhere.
+        if (destroyRootParent->isRenderFlowThread() || destroyRootParent->isAnonymousColumnSpanBlock())

[Julien - ping for review, 2014/12/03 23:05:00]

I would keep the 2 conditions separated as it would make it more obvious which
comments refers to what.

[mstensho (USE GERRIT), 2014/12/04 06:57:06]

Done.

             break;
 
         if (destroyRootParent->slowFirstChild() != destroyRoot || destroyRootParent->slowLastChild() != destroyRoot)