WIP: Prune the prepaint tree walk

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

Index: third_party/WebKit/Source/core/paint/ObjectPaintProperties.h
diff --git a/third_party/WebKit/Source/core/paint/ObjectPaintProperties.h b/third_party/WebKit/Source/core/paint/ObjectPaintProperties.h
index cd4e15aebdc9120826e7be08d13577e73a36377e..9d7a9a8c088ac43550de0d9cf73e4c5bf413ea37 100644
--- a/third_party/WebKit/Source/core/paint/ObjectPaintProperties.h
+++ b/third_party/WebKit/Source/core/paint/ObjectPaintProperties.h
@@ -6,6 +6,7 @@
 #define ObjectPaintProperties_h
 
 #include "core/CoreExport.h"
+#include "core/paint/PaintPropertyTreeBuilder.h"
 #include "platform/geometry/LayoutPoint.h"
 #include "platform/graphics/paint/ClipPaintPropertyNode.h"
 #include "platform/graphics/paint/EffectPaintPropertyNode.h"
@@ -124,9 +125,19 @@ class CORE_EXPORT ObjectPaintProperties {
   const PropertyTreeStateWithOffset* localBorderBoxProperties() const {
     return m_localBorderBoxProperties.get();
   }
-  void setLocalBorderBoxProperties(
+  TreeStructureChange setLocalBorderBoxProperties(
       std::unique_ptr<PropertyTreeStateWithOffset> properties) {
+    DCHECK(properties);
+    bool existingNode = !!m_localBorderBoxProperties;
     m_localBorderBoxProperties = std::move(properties);
+    return existingNode ? StructureNotChanged : StructureChanged;
+  }
+  TreeStructureChange clearLocalBorderBoxProperties() {
+    if (m_localBorderBoxProperties) {
+      m_localBorderBoxProperties = nullptr;
+      return StructureChanged;
+    }
+    return StructureNotChanged;
   }
 
   // This is the complete set of property nodes and paint offset that can be
@@ -136,75 +147,84 @@ class CORE_EXPORT ObjectPaintProperties {
   // invalidation.
   ObjectPaintProperties::PropertyTreeStateWithOffset contentsProperties() const;
 
-  void clearPaintOffsetTranslation() { m_paintOffsetTranslation = nullptr; }
-  void clearTransform() { m_transform = nullptr; }
-  void clearEffect() { m_effect = nullptr; }
-  void clearCssClip() { m_cssClip = nullptr; }
-  void clearCssClipFixedPosition() { m_cssClipFixedPosition = nullptr; }
-  void clearInnerBorderRadiusClip() { m_innerBorderRadiusClip = nullptr; }
-  void clearOverflowClip() { m_overflowClip = nullptr; }
-  void clearLocalBorderBoxProperties() { m_localBorderBoxProperties = nullptr; }
-  void clearPerspective() { m_perspective = nullptr; }
-  void clearSvgLocalToBorderBoxTransform() {
-    m_svgLocalToBorderBoxTransform = nullptr;
-  }
-  void clearScrollTranslation() { m_scrollTranslation = nullptr; }
-  void clearScrollbarPaintOffset() { m_scrollbarPaintOffset = nullptr; }
-  void clearScroll() { m_scroll = nullptr; }
+  TreeStructureChange clearPaintOffsetTranslation() {
+    return clear(m_paintOffsetTranslation);
+  }
+  TreeStructureChange clearTransform() { return clear(m_transform); }
+  TreeStructureChange clearEffect() { return clear(m_effect); }
+  TreeStructureChange clearCssClip() { return clear(m_cssClip); }
+  TreeStructureChange clearCssClipFixedPosition() {
+    return clear(m_cssClipFixedPosition);
+  }
+  TreeStructureChange clearInnerBorderRadiusClip() {
+    return clear(m_innerBorderRadiusClip);
+  }
+  TreeStructureChange clearOverflowClip() { return clear(m_overflowClip); }
+  TreeStructureChange clearPerspective() { return clear(m_perspective); }
+  TreeStructureChange clearSvgLocalToBorderBoxTransform() {
+    return clear(m_svgLocalToBorderBoxTransform);
+  }
+  TreeStructureChange clearScrollTranslation() {
+    return clear(m_scrollTranslation);
+  }
+  TreeStructureChange clearScrollbarPaintOffset() {
+    return clear(m_scrollbarPaintOffset);
+  }
+  TreeStructureChange clearScroll() { return clear(m_scroll); }
 
   template <typename... Args>
-  void updatePaintOffsetTranslation(Args&&... args) {
-    updateProperty(m_paintOffsetTranslation, std::forward<Args>(args)...);
+  TreeStructureChange updatePaintOffsetTranslation(Args&&... args) {
+    return update(m_paintOffsetTranslation, std::forward<Args>(args)...);
   }
   template <typename... Args>
-  void updateTransform(Args&&... args) {
-    updateProperty(m_transform, std::forward<Args>(args)...);
+  TreeStructureChange updateTransform(Args&&... args) {
+    return update(m_transform, std::forward<Args>(args)...);
   }
   template <typename... Args>
-  void updatePerspective(Args&&... args) {
-    updateProperty(m_perspective, std::forward<Args>(args)...);
+  TreeStructureChange updatePerspective(Args&&... args) {
+    return update(m_perspective, std::forward<Args>(args)...);
   }
   template <typename... Args>
-  void updateSvgLocalToBorderBoxTransform(Args&&... args) {
+  TreeStructureChange updateSvgLocalToBorderBoxTransform(Args&&... args) {
     DCHECK(!scrollTranslation()) << "SVG elements cannot scroll so there "
                                     "should never be both a scroll translation "
                                     "and an SVG local to border box transform.";
-    updateProperty(m_svgLocalToBorderBoxTransform, std::forward<Args>(args)...);
+    return update(m_svgLocalToBorderBoxTransform, std::forward<Args>(args)...);
   }
   template <typename... Args>
-  void updateScrollTranslation(Args&&... args) {
+  TreeStructureChange updateScrollTranslation(Args&&... args) {
     DCHECK(!svgLocalToBorderBoxTransform())
         << "SVG elements cannot scroll so there should never be both a scroll "
            "translation and an SVG local to border box transform.";
-    updateProperty(m_scrollTranslation, std::forward<Args>(args)...);
+    return update(m_scrollTranslation, std::forward<Args>(args)...);
   }
   template <typename... Args>
-  void updateScrollbarPaintOffset(Args&&... args) {
-    updateProperty(m_scrollbarPaintOffset, std::forward<Args>(args)...);
+  TreeStructureChange updateScrollbarPaintOffset(Args&&... args) {
+    return update(m_scrollbarPaintOffset, std::forward<Args>(args)...);
   }
   template <typename... Args>
-  void updateScroll(Args&&... args) {
-    updateProperty(m_scroll, std::forward<Args>(args)...);
+  TreeStructureChange updateScroll(Args&&... args) {
+    return update(m_scroll, std::forward<Args>(args)...);
   }
   template <typename... Args>
-  void updateEffect(Args&&... args) {
-    updateProperty(m_effect, std::forward<Args>(args)...);
+  TreeStructureChange updateEffect(Args&&... args) {
+    return update(m_effect, std::forward<Args>(args)...);
   }
   template <typename... Args>
-  void updateCssClip(Args&&... args) {
-    updateProperty(m_cssClip, std::forward<Args>(args)...);
+  TreeStructureChange updateCssClip(Args&&... args) {
+    return update(m_cssClip, std::forward<Args>(args)...);
   }
   template <typename... Args>
-  void updateCssClipFixedPosition(Args&&... args) {
-    updateProperty(m_cssClipFixedPosition, std::forward<Args>(args)...);
+  TreeStructureChange updateCssClipFixedPosition(Args&&... args) {
+    return update(m_cssClipFixedPosition, std::forward<Args>(args)...);
   }
   template <typename... Args>
-  void updateInnerBorderRadiusClip(Args&&... args) {
-    updateProperty(m_innerBorderRadiusClip, std::forward<Args>(args)...);
+  TreeStructureChange updateInnerBorderRadiusClip(Args&&... args) {
+    return update(m_innerBorderRadiusClip, std::forward<Args>(args)...);
   }
   template <typename... Args>
-  void updateOverflowClip(Args&&... args) {
-    updateProperty(m_overflowClip, std::forward<Args>(args)...);
+  TreeStructureChange updateOverflowClip(Args&&... args) {
+    return update(m_overflowClip, std::forward<Args>(args)...);
   }
 
 #if DCHECK_IS_ON()
@@ -253,11 +273,22 @@ class CORE_EXPORT ObjectPaintProperties {
   ObjectPaintProperties() {}
 
   template <typename PaintPropertyNode, typename... Args>
-  void updateProperty(RefPtr<PaintPropertyNode>& field, Args&&... args) {
-    if (field)
+  TreeStructureChange update(RefPtr<PaintPropertyNode>& field, Args&&... args) {
+    if (field) {
       field->update(std::forward<Args>(args)...);
-    else
-      field = PaintPropertyNode::create(std::forward<Args>(args)...);
+      return StructureNotChanged;
+    }
+    field = PaintPropertyNode::create(std::forward<Args>(args)...);
+    return StructureChanged;
+  }
+
+  template <typename PaintPropertyNode>
+  TreeStructureChange clear(RefPtr<PaintPropertyNode>& field) {
+    if (field) {
+      field = nullptr;
+      return StructureChanged;
+    }
+    return StructureNotChanged;
   }
 
   RefPtr<TransformPaintPropertyNode> m_paintOffsetTranslation;