Clean up forward declarations in core/rendering and core/painting

Source/core/paint/BlockFlowPainter.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BlockFlowPainter_h
 #define BlockFlowPainter_h
 
 namespace blink {
 
-class FloatingObject;
 class LayoutPoint;
 struct PaintInfo;
 class RenderBlockFlow;
 
 class BlockFlowPainter {
 public:
     BlockFlowPainter(RenderBlockFlow& renderBlockFlow) : m_renderBlockFlow(renderBlockFlow) { }
     void paintFloats(PaintInfo&, const LayoutPoint&, bool preservePhase);
 
 private:
     RenderBlockFlow& m_renderBlockFlow;
 };
 
 } // namespace blink
 
 #endif // BlockFlowPainter_h