WIP: Prune the prepaint tree walk

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

Index: third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.h
diff --git a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.h b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.h
index 29d89b7dfd80bde2a663b560b189156ba1447b57..9f6fd6575f6764cad8d94665bd054533be86283f 100644
--- a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.h
+++ b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.h
@@ -14,6 +14,13 @@
 
 namespace blink {
 
+enum TreeStructureChange {
+  // Nodes were not added or removed.
+  StructureNotChanged = false,
+  // Nodes were added or removed.
+  StructureChanged = true
+};
+
 class FrameView;
 class LayoutObject;
 
@@ -84,45 +91,54 @@ class PaintPropertyTreeBuilder {
   PaintPropertyTreeBuilderContext setupInitialContext();
   // Update the paint properties for a frame and ensure the context is up to
   // date.
-  void updateProperties(FrameView&, PaintPropertyTreeBuilderContext&);
+  TreeStructureChange updateProperties(FrameView&,
+                                       PaintPropertyTreeBuilderContext&);
 
   // Update the paint properties that affect this object (e.g., properties like
   // paint offset translation) and ensure the context is up to date.
-  void updatePropertiesForSelf(const LayoutObject&,
-                               PaintPropertyTreeBuilderContext&);
+  TreeStructureChange updatePropertiesForSelf(const LayoutObject&,
+                                              PaintPropertyTreeBuilderContext&);
   // Update the paint properties that affect children of this object (e.g.,
   // scroll offset transform) and ensure the context is up to date.
-  void updatePropertiesForChildren(const LayoutObject&,
-                                   PaintPropertyTreeBuilderContext&);
+  TreeStructureChange updatePropertiesForChildren(
+      const LayoutObject&,
+      PaintPropertyTreeBuilderContext&);
 
  private:
-  static void updatePaintOffsetTranslation(const LayoutObject&,
-                                           PaintPropertyTreeBuilderContext&);
-  static void updateTransform(const LayoutObject&,
-                              PaintPropertyTreeBuilderContext&);
-  static void updateTransformForNonRootSVG(const LayoutObject&,
-                                           PaintPropertyTreeBuilderContext&);
-  static void updateEffect(const LayoutObject&,
-                           PaintPropertyTreeBuilderContext&);
-  static void updateCssClip(const LayoutObject&,
-                            PaintPropertyTreeBuilderContext&);
-  static void updateLocalBorderBoxContext(const LayoutObject&,
+  static void updatePaintOffsetTranslation(
+      const LayoutObject&,
+      PaintPropertyTreeBuilderContext&,
+      bool& treeStructureChanged);
+  static TreeStructureChange updateTransform(const LayoutObject&,
+                                             PaintPropertyTreeBuilderContext&);
+  static TreeStructureChange updateTransformForNonRootSVG(
+      const LayoutObject&,
+      PaintPropertyTreeBuilderContext&);
+  static TreeStructureChange updateEffect(const LayoutObject&,
                                           PaintPropertyTreeBuilderContext&);
-  static void updateScrollbarPaintOffset(
+  static TreeStructureChange updateCssClip(const LayoutObject&,
+                                           PaintPropertyTreeBuilderContext&);
+  static TreeStructureChange updateLocalBorderBoxContext(
+      const LayoutObject&,
+      PaintPropertyTreeBuilderContext&);
+  static TreeStructureChange updateScrollbarPaintOffset(
       const LayoutObject&,
       const PaintPropertyTreeBuilderContext&);
-  static void updateOverflowClip(const LayoutObject&,
-                                 PaintPropertyTreeBuilderContext&);
-  static void updatePerspective(const LayoutObject&,
-                                PaintPropertyTreeBuilderContext&);
-  static void updateSvgLocalToBorderBoxTransform(
+  static TreeStructureChange updateOverflowClip(
+      const LayoutObject&,
+      PaintPropertyTreeBuilderContext&);
+  static TreeStructureChange updatePerspective(
+      const LayoutObject&,
+      PaintPropertyTreeBuilderContext&);
+  static TreeStructureChange updateSvgLocalToBorderBoxTransform(
+      const LayoutObject&,
+      PaintPropertyTreeBuilderContext&);
+  static TreeStructureChange updateScrollAndScrollTranslation(
       const LayoutObject&,
       PaintPropertyTreeBuilderContext&);
-  static void updateScrollAndScrollTranslation(
+  static TreeStructureChange updateOutOfFlowContext(
       const LayoutObject&,
       PaintPropertyTreeBuilderContext&);
-  static void updateOutOfFlowContext(const LayoutObject&,
-                                     PaintPropertyTreeBuilderContext&);
 };
 
 }  // namespace blink