Implement a non-recursive PrePaint treewalk

third_party/WebKit/Source/core/paint/PrePaintTreeWalk.h

 // Copyright 2015 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 PrePaintTreeWalk_h
 #define PrePaintTreeWalk_h
 
 #include "core/paint/ClipRect.h"
 #include "core/paint/PaintInvalidator.h"
 #include "core/paint/PaintPropertyTreeBuilder.h"
 
 namespace blink {
 
 class FrameView;
 class GeometryMapper;
 class LayoutObject;
+class LayoutView;
 struct PrePaintTreeWalkContext;
 
 // This class walks the whole layout tree, beginning from the root FrameView,
 // across frame boundaries. Helper classes are called for each tree node to
 // perform actual actions.  It expects to be invoked in InPrePaint phase.
 class PrePaintTreeWalk {
  public:
   PrePaintTreeWalk(GeometryMapper& geometryMapper)
       : m_paintInvalidator(geometryMapper), m_geometryMapper(geometryMapper) {}
   void walk(FrameView& rootFrame);
 
  private:
+  // Walk a FrameView and the entire LayoutObject tree it contains.
   void walk(FrameView&, const PrePaintTreeWalkContext&);
-  void walk(const LayoutObject&, const PrePaintTreeWalkContext&);
+  // Walk a LayoutView and the entire LayoutObject tree below.
+  void walk(const LayoutView&, const PrePaintTreeWalkContext&);
+
+  // Walk a single LayoutObject.
+  void walkObject(const LayoutObject&, PrePaintTreeWalkContext&);
 
   // Invalidates paint-layer painting optimizations, such as subsequence caching
   // and empty paint phase optimizations if clips from the context have changed.
   void invalidatePaintLayerOptimizationsIfNeeded(const LayoutObject&,
                                                  PrePaintTreeWalkContext&);
 
   // Returns the clip applied to children for the given
   // contaiing block context + effect, in the space of ancestorState adjusted
   // by ancestorPaintOffset. Sets hasClip to true if a clip was applied.
   FloatClipRect clipRectForContext(
       const PaintPropertyTreeBuilderContext::ContainingBlockContext&,
       const EffectPaintPropertyNode*,
       const PropertyTreeState& ancestorState,
       const LayoutPoint& ancestorPaintOffset,
       bool& hasClip);
 
   // Returns true if the tree walk should stop before processing this object.
   bool shouldEndWalkBefore(const LayoutObject&, const PrePaintTreeWalkContext&);
 
   PaintPropertyTreeBuilder m_propertyTreeBuilder;
   PaintInvalidator m_paintInvalidator;
   GeometryMapper& m_geometryMapper;
 };
 
 }  // namespace blink
 
 #endif  // PrePaintTreeWalk_h