[SPInvalidation] Fix PrePaintTreeWalk for multicol spanner

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

Index: third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
index 5a627a037a844570a70db6d54df4fbe64439033e..3e8e63a2ce6fdaf4f8cb42b2f5e5dce0e79a1a75 100644
--- a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
@@ -658,6 +658,45 @@ void PaintPropertyTreeBuilder::updateOutOfFlowContext(
     properties->clearCssClipFixedPosition();
 }
 
+// Override ContainerContext based on the properties of a container that was
+// previously walked in a subtree other than the current subtree being walked.
+// Used for out-of-flow positioned descendants of multi-column spanner when
+// the container is not in the normal tree walk order.
+// For example:
+// <div id="columns" style="columns: 2">
+//   <div id="relative" style="position: relative">
+//     <div id="spanner" style="column-span: all">
+//       <div id="absolute" style="position: absolute"></div>
+//     </div>
+//   </div>
+// <div>
+// The real container of "absolute" is "relative" which is not in the tree-walk
+// order of "columns" -> spanner placeholder -> spanner -> absolute. Here we
+// rebuild a ContainerContext based on the properties of "relative" for
+// "absolute".
+static void overrideContainerContextFromContainer(
+    const LayoutObject& container,
+    PaintPropertyTreeBuilderContext::ContainerContext& context) {
+  // The container is never a LayoutInline. In the above example, if we change
+  // the container to an inline, there must be an anonymous blocks created
+  // because the spanner is always a block.
+  DCHECK(container.isLayoutBlock());
+
+  const auto* properties =
+      container.objectPaintProperties()->localBorderBoxProperties();
+  DCHECK(properties);
+
+  context.transform = properties->propertyTreeState.transform();
+  context.paintOffset = properties->paintOffset;
+  context.shouldFlattenInheritedTransform =
+      context.transform && context.transform->flattensInheritedTransform();
+  context.renderingContextID =
+      context.transform ? context.transform->renderingContextID() : 0;
+  context.clip = properties->propertyTreeState.clip();
+  context.scroll = const_cast<ScrollPaintPropertyNode*>(
+      properties->propertyTreeState.scroll());
+}
+
 static void deriveBorderBoxFromContainerContext(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
@@ -673,9 +712,23 @@ static void deriveBorderBoxFromContainerContext(
       context.current.paintOffset += boxModelObject.offsetForInFlowPosition();
       break;
     case AbsolutePosition: {
-      context.current = context.absolutePosition;
+      if (context.isUnderMultiColumnSpanner) {
+        const LayoutObject* container = boxModelObject.container();
+        if (container != context.containerForAbsolutePosition) {
+          // The container of the absolute-position is not in the normal tree-
+          // walk order.
+          context.containerForAbsolutePosition =
+              toLayoutBoxModelObject(container);
+          overrideContainerContextFromContainer(*container, context.current);
+        }
+      } else {
+        DCHECK(context.containerForAbsolutePosition ==
+               boxModelObject.container());
+        context.current = context.absolutePosition;
+      }
 
-      // Absolutely positioned content in an inline should be positioned relative to the inline.
+      // Absolutely positioned content in an inline should be positioned
+      // relative to the inline.
       const LayoutObject* container = context.containerForAbsolutePosition;
       if (container && container->isInFlowPositioned() &&
           container->isLayoutInline()) {
@@ -690,7 +743,14 @@ static void deriveBorderBoxFromContainerContext(
       context.current.paintOffset += boxModelObject.offsetForInFlowPosition();
       break;
     case FixedPosition:
-      context.current = context.fixedPosition;
+      if (context.isUnderMultiColumnSpanner) {
+        // The container of the fixed-position object may or may not be in the
+        // normal tree-walk order.
+        overrideContainerContextFromContainer(*boxModelObject.container(),
+                                              context.current);
+      } else {
+        context.current = context.fixedPosition;
+      }
       break;
     default:
       ASSERT_NOT_REACHED();