Generate scroll/clip display item hierarchy for SPv2

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"
 #include "platform/graphics/paint/ClipDisplayItem.h"
 #include "platform/graphics/paint/DisplayItem.h"
 #include "wtf/Vector.h"
 
 namespace blink {
 
 class ClipRect;
 class GraphicsContext;
+class LayoutBox;
 class LayoutBoxModelObject;
 
 class CORE_EXPORT LayerClipRecorder {
     WTF_MAKE_FAST_ALLOCATED(LayerClipRecorder);
 public:
 
     enum BorderRadiusClippingRule { IncludeSelfForBorderRadius, DoNotIncludeSelfForBorderRadius };
 
     // Set rounded clip rectangles defined by border radii all the way from the DeprecatedPaintLayerPaintingInfo
     // "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&, const LayoutBoxModelObject&, DisplayItem::Type, const ClipRect&, const DeprecatedPaintLayerPaintingInfo*, const LayoutPoint& fragmentOffset, PaintLayerFlags, BorderRadiusClippingRule = IncludeSelfForBorderRadius);
+
+    // Note: This constructor is designed for SPv2, and has drastically different semantics than
+    // the other version above. In the old layer painting model, a layer is responsible for
+    // calculating the accumulated clip from ancestors, and applies the clip to itself.
+    // In SPv2, it is the layer that establishes overflow clipping who is responsible to clip
+    // its descendants. This constructor takes a layer, and only issues clip for that layer.
+    LayerClipRecorder(GraphicsContext&, const LayoutBox&, const LayoutPoint& paintOffset);

[pdr., 2015/09/03 06:16:59]

Because the two modes for LayerClipRecorder are so different, lets add a second
class in this file called LayerClipRecorderForSlimmingPaintV2 instead of
re-using the existing class. The comment is very helpful so lets keep it, just
tweaked for a new class.

[trchen, 2015/09/04 06:10:15]

Done.

 
     ~LayerClipRecorder();
 
 private:
 
     void collectRoundedRectClips(DeprecatedPaintLayer&, const DeprecatedPaintLayerPaintingInfo& localPaintingInfo, GraphicsContext&, const LayoutPoint& fragmentOffset, PaintLayerFlags,
         BorderRadiusClippingRule, Vector<FloatRoundedRect>& roundedRectClips);
 
     GraphicsContext& m_graphicsContext;
     const LayoutBoxModelObject& m_layoutObject;
     DisplayItem::Type m_clipType;
 };
 
 } // namespace blink
 
 #endif // LayerClipRecorder_h