RenderBlock::isSelfCollapsingBlock() should only be used when an object does not require layout.

Source/core/rendering/RenderTextControlPlaceholder.h

Index: Source/core/rendering/RenderTextControlPlaceholder.h
diff --git a/Source/core/rendering/RenderTableCaption.h b/Source/core/rendering/RenderTextControlPlaceholder.h
similarity index 51%
copy from Source/core/rendering/RenderTableCaption.h
copy to Source/core/rendering/RenderTextControlPlaceholder.h
index 35755a9d03b26632206ecc341a7ff7cb53b11a12..58ddba81c543bf88e7f4544add9ab8f36ecdb9e4 100644
--- a/Source/core/rendering/RenderTableCaption.h
+++ b/Source/core/rendering/RenderTextControlPlaceholder.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2011 Robert Hogan <robert@roberthogan.net>
+ * Copyright (C) 2014 Robert Hogan <robert@roberthogan.net>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ -17,34 +17,26 @@
  * Boston, MA 02110-1301, USA.
  */
 
-#ifndef RenderTableCaption_h
-#define RenderTableCaption_h
+#ifndef RenderTextControlPlaceholder_h
+#define RenderTextControlPlaceholder_h
 
 #include "core/rendering/RenderBlockFlow.h"
 
 namespace WebCore {
 
-class RenderTable;
 
-class RenderTableCaption FINAL : public RenderBlockFlow {
+class RenderTextControlPlaceholder FINAL : public RenderBlockFlow {
 public:
-    explicit RenderTableCaption(Element*);
-    virtual ~RenderTableCaption();
-    virtual LayoutUnit containingBlockLogicalWidthForContent() const OVERRIDE;
-
-private:
-    virtual bool isTableCaption() const OVERRIDE { return true; }
-
-    virtual bool supportsPartialLayout() const OVERRIDE { return false; }
-
-    virtual void insertedIntoTree() OVERRIDE;
-    virtual void willBeRemovedFromTree() OVERRIDE;
-
-    RenderTable* table() const;
+    explicit RenderTextControlPlaceholder(Element*);
+    virtual ~RenderTextControlPlaceholder();
+
+    // Placeholder elements are not laid out until the dimensions of their parent text control are known,
+    // so they don't get layout until their parent has had layout. This is a problem when we have iterated
+    // a parent's children and want to call isSelfCollapsingBlock. Fortunately since placeholder elements
+    // only exist when they have content we can always enforce the rule that they are never self-collapsing.
+    virtual bool isSelfCollapsingBlock() const OVERRIDE FINAL { return false; }
 };
 
-DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderTableCaption, isTableCaption());
-
 } // namespace WebCore
 
-#endif // RenderTableCaption_h
+#endif // RenderTextControlPlaceholder_h