No longer any need to delete the line box tree on our own.

Source/core/layout/LayoutMultiColumnFlowThread.cpp

Index: Source/core/layout/LayoutMultiColumnFlowThread.cpp
diff --git a/Source/core/layout/LayoutMultiColumnFlowThread.cpp b/Source/core/layout/LayoutMultiColumnFlowThread.cpp
index 478f89d9d701fd067c66d0e799cfbdb7284497dc..a9660fcfc08fbe8e6d1665a66ba67104b4a2ab53 100644
--- a/Source/core/layout/LayoutMultiColumnFlowThread.cpp
+++ b/Source/core/layout/LayoutMultiColumnFlowThread.cpp
@@ -255,12 +255,6 @@ void LayoutMultiColumnFlowThread::evacuateAndDestroy()
     multicolContainer->resetMultiColumnFlowThread();
     moveAllChildrenTo(multicolContainer, true);
 
-    // FIXME: it's scary that neither destroy() nor the move*Children* methods take care of this,
-    // and instead leave you with dangling root line box pointers. But since this is how it is done
-    // in other parts of the code that deal with reparenting layoutObjects, let's do the cleanup on our
-    // own here as well.
-    deleteLineBoxTree();

[leviw_travelin_and_unemployed, 2015/09/11 15:38:39]

Perhaps assert !firstLineBox?

[mstensho (USE GERRIT), 2015/09/11 18:03:49]

And readers of the code will go "huh?", but I can add a comment too. :)

Done.

-
     destroy();
 }