The ASSERT in appendNode() should not fire when OBJECTS are cloned.

Source/core/editing/CompositeEditCommand.cpp

 /*
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  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
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@@ skipping 342 matching lines @@
         // Mutation events (bug 22634) from the text node insertion may have removed the refChild
         if (!refChild->inDocument())
             return;
         insertNodeBefore(insertChild, refChild);
     } else
         insertNodeAfter(insertChild, refChild);
 }
 
 void CompositeEditCommand::appendNode(PassRefPtrWillBeRawPtr<Node> node, PassRefPtrWillBeRawPtr<ContainerNode> parent)
 {
-    ASSERT(canHaveChildrenForEditing(parent.get()));
+    // The useFallbackContent() is not set for cloned <object> nodes.
+    ASSERT(canHaveChildrenForEditing(parent.get())
+        || (parent->isElementNode() && toElement(parent.get())->tagQName() == objectTag));

[yosin_UTC9, 2014/11/20 01:26:41]

Could you add a comment why we check OBJECT element?

Note: We have OBJECT element here if |start| or |end| position are in OBJECT's
fallback content in |CompositeEditCommand::cloneParagraphUnderNewElement()|.

     applyCommandToComposite(AppendNodeCommand::create(parent, node));
 }
 
 void CompositeEditCommand::removeChildrenInRange(PassRefPtrWillBeRawPtr<Node> node, unsigned from, unsigned to)
 {
     WillBeHeapVector<RefPtrWillBeMember<Node>> children;
     Node* child = NodeTraversal::childAt(*node, from);
     for (unsigned i = from; child && i < to; i++, child = child->nextSibling())
         children.append(child);
 
@@ skipping 1119 matching lines @@
 }
 
 void CompositeEditCommand::trace(Visitor* visitor)
 {
     visitor->trace(m_commands);
     visitor->trace(m_composition);
     EditCommand::trace(visitor);
 }
 
 } // namespace blink