[SPv2] Move PaintPropertyTreeBuilder state for containing blocks into a struct.

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/TransformPaintPropertyNode.h"
 #include "wtf/RefPtr.h"
 
 namespace blink {
 
 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 {
-    PaintPropertyTreeBuilderContext()
-        : currentTransform(nullptr)
-        , currentClip(nullptr)
-        , transformForAbsolutePosition(nullptr)
-        , containerForAbsolutePosition(nullptr)
-        , clipForAbsolutePosition(nullptr)
-        , transformForFixedPosition(nullptr)
-        , clipForFixedPosition(nullptr)
-        , currentEffect(nullptr) { }
+    // State that propagates on the containing block chain (and so is adjusted
+    // when an absolute or fixed position object is encountered).
+    struct ContainingBlockContext {
+        // The combination of a transform and paint offset describes a linear space.
+        // When a layout object recur to its children, the main context is expected to refer
+        // the object's border box, then the callee will derive its own border box by translating
+        // the space with its own layout location.
+        TransformPaintPropertyNode* transform = nullptr;
+        LayoutPoint paintOffset;
+        // The clip node describes the accumulated raster clip for the current subtree.
+        // Note that the computed raster region in canvas space for a clip node is independent from
+        // the transform and paint offset above. Also the actual raster region may be affected
+        // by layerization and occlusion tracking.
+        ClipPaintPropertyNode* clip = nullptr;
+    };
 
-    // The combination of a transform and paint offset describes a linear space.
-    // When a layout object recur to its children, the main context is expected to refer
-    // the object's border box, then the callee will derive its own border box by translating
-    // the space with its own layout location.
-    TransformPaintPropertyNode* currentTransform;
-    LayoutPoint paintOffset;
-    // The clip node describes the accumulated raster clip for the current subtree.
-    // Note that the computed raster region in canvas space for a clip node is independent from
-    // the transform and paint offset above. Also the actual raster region may be affected
-    // by layerization and occlusion tracking.
-    ClipPaintPropertyNode* currentClip;
+    ContainingBlockContext current;
 
     // Separate context for out-of-flow positioned and fixed positioned elements are needed
     // because they don't use DOM parent as their containing block.
     // These additional contexts normally pass through untouched, and are only copied from
     // the main context when the current element serves as the containing block of corresponding
     // positioned descendants.
     // Overflow clips are also inherited by containing block tree instead of DOM tree, thus they
     // are included in the additional context too.
-    TransformPaintPropertyNode* transformForAbsolutePosition;
-    LayoutPoint paintOffsetForAbsolutePosition;
-    const LayoutObject* containerForAbsolutePosition;
-    ClipPaintPropertyNode* clipForAbsolutePosition;
+    ContainingBlockContext absolutePosition;
+    const LayoutObject* containerForAbsolutePosition = nullptr;
 
-    TransformPaintPropertyNode* transformForFixedPosition;
-    LayoutPoint paintOffsetForFixedPosition;
-    ClipPaintPropertyNode* clipForFixedPosition;
+    ContainingBlockContext fixedPosition;
 
     // The effect hierarchy is applied by the stacking context tree. It is guaranteed that every
     // DOM descendant is also a stacking context descendant. Therefore, we don't need extra
     // bookkeeping for effect nodes and can generate the effect tree from a DOM-order traversal.
-    EffectPaintPropertyNode* currentEffect;
+    EffectPaintPropertyNode* currentEffect = nullptr;
 };
 
 // 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:
     void buildTreeRootNodes(FrameView&, PaintPropertyTreeBuilderContext&);
     void buildTreeNodes(FrameView&, PaintPropertyTreeBuilderContext&);
     void buildTreeNodes(const LayoutObject&, PaintPropertyTreeBuilderContext&);
 
 private:
     static void updatePaintOffsetTranslation(const LayoutObject&, PaintPropertyTreeBuilderContext&);
     static void updateTransform(const LayoutObject&, PaintPropertyTreeBuilderContext&);
     static void updateEffect(const LayoutObject&, PaintPropertyTreeBuilderContext&);
     static void updateCssClip(const LayoutObject&, PaintPropertyTreeBuilderContext&);
     static void updateLocalBorderBoxContext(const LayoutObject&, const PaintPropertyTreeBuilderContext&);
     static void updateScrollbarPaintOffset(const LayoutObject&, const PaintPropertyTreeBuilderContext&);
     static void updateOverflowClip(const LayoutObject&, PaintPropertyTreeBuilderContext&);
     static void updatePerspective(const LayoutObject&, PaintPropertyTreeBuilderContext&);
     static void updateSvgLocalToBorderBoxTransform(const LayoutObject&, PaintPropertyTreeBuilderContext&);
     static void updateScrollTranslation(const LayoutObject&, PaintPropertyTreeBuilderContext&);
     static void updateOutOfFlowContext(const LayoutObject&, PaintPropertyTreeBuilderContext&);
 };
 
 } // namespace blink
 
 #endif // PaintPropertyTreeBuilder_h