Implement a non-recursive PrePaint treewalk

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

Index: third_party/WebKit/Source/core/paint/PrePaintTreeWalk.h
diff --git a/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.h b/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.h
index 634292466820fdcb00809a6b1e83e483e73c4e1a..0333958dd73e33e52e103de181b0345e52cfd389 100644
--- a/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.h
+++ b/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.h
@@ -14,6 +14,7 @@ namespace blink {
 class FrameView;
 class GeometryMapper;
 class LayoutObject;
+class LayoutView;
 struct PrePaintTreeWalkContext;
 
 // This class walks the whole layout tree, beginning from the root FrameView,
@@ -26,8 +27,13 @@ class PrePaintTreeWalk {
   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.