WIP: Prune the prepaint tree walk

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.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 PaintPropertyTreeBuilder_h
 #define PaintPropertyTreeBuilder_h
 
 #include "platform/geometry/LayoutPoint.h"
 #include "platform/graphics/paint/ClipPaintPropertyNode.h"
 #include "platform/graphics/paint/EffectPaintPropertyNode.h"
 #include "platform/graphics/paint/ScrollPaintPropertyNode.h"
 #include "platform/graphics/paint/TransformPaintPropertyNode.h"
 #include "wtf/RefPtr.h"
 
 namespace blink {
 
+enum TreeStructureChange {
+  // Nodes were not added or removed.
+  StructureNotChanged = false,
+  // Nodes were added or removed.
+  StructureChanged = true
+};
+
 class FrameView;
 class LayoutObject;
 
 // The context for PaintPropertyTreeBuilder.
 // It's responsible for bookkeeping tree state in other order, for example, the
 // most recent position container seen.
 struct PaintPropertyTreeBuilderContext {
   // State that propagates on the containing block chain (and so is adjusted
   // when an absolute or fixed position object is encountered).
   struct ContainingBlockContext {
@@ skipping 50 matching lines @@
 // Creates paint property tree nodes for special things in the layout tree.
 // Special things include but not limit to: overflow clip, transform, fixed-pos,
 // animation, mask, filter, ... etc.
 // It expects to be invoked for each layout tree node in DOM order during
 // InPrePaint phase.
 class PaintPropertyTreeBuilder {
  public:
   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&,
+  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 TreeStructureChange updateCssClip(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&,
-                                          PaintPropertyTreeBuilderContext&);
-  static void updateScrollbarPaintOffset(
+  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 void updateScrollAndScrollTranslation(
+  static TreeStructureChange updatePerspective(
       const LayoutObject&,
       PaintPropertyTreeBuilderContext&);
-  static void updateOutOfFlowContext(const LayoutObject&,
-                                     PaintPropertyTreeBuilderContext&);
+  static TreeStructureChange updateSvgLocalToBorderBoxTransform(
+      const LayoutObject&,
+      PaintPropertyTreeBuilderContext&);
+  static TreeStructureChange updateScrollAndScrollTranslation(
+      const LayoutObject&,
+      PaintPropertyTreeBuilderContext&);
+  static TreeStructureChange updateOutOfFlowContext(
+      const LayoutObject&,
+      PaintPropertyTreeBuilderContext&);
 };
 
 }  // namespace blink
 
 #endif  // PaintPropertyTreeBuilder_h