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

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 118763fc8dd13dd5435b6930927c4b941c62e3c0..16f07086d7c79ffe1a76b6eefae797928862a7c9 100644
--- a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.h
+++ b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.h
@@ -20,27 +20,23 @@ class LayoutObject;
 // 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.
@@ -49,19 +45,15 @@ struct PaintPropertyTreeBuilderContext {
     // 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.