Allow certain SP recorder classes to defer their "begin" operation.

Source/core/paint/LayerClipRecorder.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 LayerClipRecorder_h
 #define LayerClipRecorder_h
 
 #include "core/CoreExport.h"
 #include "core/paint/DeprecatedPaintLayerPaintingInfo.h"
 #include "core/paint/PaintPhase.h"
@@ skipping 16 matching lines @@
     // "root" layer down to the specified layer (or the parent of said layer, in case
     // BorderRadiusClippingRule says to skip self). fragmentOffset is used for multicol, to specify
     // the translation required to get from flow thread coordinates to visual coordinates for a
     // certain column.
     // FIXME: The BorderRadiusClippingRule parameter is really useless now. If we want to skip self,
     // why not just supply the parent layer as the first parameter instead?
     // FIXME: The ClipRect passed is in visual coordinates (not flow thread coordinates), but at the
     // same time we pass a fragmentOffset, so that we can translate from flow thread coordinates to
     // visual coordinates. This may look rather confusing/redundant, but it is needed for rounded
     // border clipping. Would be nice to clean up this.
-    explicit LayerClipRecorder(GraphicsContext&, const LayoutBoxModelObject&, DisplayItem::Type, const ClipRect&, const DeprecatedPaintLayerPaintingInfo* localPaintingInfo, const LayoutPoint& fragmentOffset, PaintLayerFlags, BorderRadiusClippingRule = IncludeSelfForBorderRadius);
+    LayerClipRecorder(GraphicsContext&, DisplayItem::Type);
+    LayerClipRecorder(GraphicsContext&, const LayoutBoxModelObject&, DisplayItem::Type, const ClipRect&, const DeprecatedPaintLayerPaintingInfo* localPaintingInfo, const LayoutPoint& fragmentOffset, PaintLayerFlags, BorderRadiusClippingRule = IncludeSelfForBorderRadius);
+    ~LayerClipRecorder();
 
-    ~LayerClipRecorder();
+    void begin(const LayoutBoxModelObject& layoutObject, const ClipRect&, const DeprecatedPaintLayerPaintingInfo* localPaintingInfo, const LayoutPoint& fragmentOffset, PaintLayerFlags, BorderRadiusClippingRule = IncludeSelfForBorderRadius);
 
 private:
 
     void collectRoundedRectClips(DeprecatedPaintLayer&, const DeprecatedPaintLayerPaintingInfo& localPaintingInfo, GraphicsContext&, const LayoutPoint& fragmentOffset, PaintLayerFlags,
         BorderRadiusClippingRule, Vector<FloatRoundedRect>& roundedRectClips);
 
     GraphicsContext& m_graphicsContext;
-    const LayoutBoxModelObject& m_layoutObject;
+    const LayoutBoxModelObject* m_layoutObject;
     DisplayItem::Type m_clipType;
+    bool m_engaged;
 };
 
 } // namespace blink
 
 #endif // LayerClipRecorder_h