*** NOT FOR LANDING *** mapLocalToContainer and offsetFromContainer cleanup.

Source/core/layout/LayoutObject.cpp

Index: Source/core/layout/LayoutObject.cpp
diff --git a/Source/core/layout/LayoutObject.cpp b/Source/core/layout/LayoutObject.cpp
index abd4d61201124cc82585b605cd753adc344d9950..7054ed37332a49fc9c6fc1a9a480dc596a89c534 100644
--- a/Source/core/layout/LayoutObject.cpp
+++ b/Source/core/layout/LayoutObject.cpp
@@ -2040,22 +2040,63 @@ void LayoutObject::mapLocalToContainer(const LayoutBoxModelObject* paintInvalida
     if (paintInvalidationContainer == this)
         return;
 
-    LayoutObject* o = parent();
+    if (paintInvalidationState && paintInvalidationState->canMapToContainer(paintInvalidationContainer)) {
+        LayoutSize offset = paintInvalidationState->paintOffset();
+        if (isBox())
+            offset += toLayoutBox(this)->locationOffset();
+        if (!isText() && style()->hasInFlowPosition() && hasLayer())
+            offset += toLayoutBoxModelObject(this)->layer()->offsetForInFlowPosition();
+        transformState.move(offset);
+        return;
+    }
+
+    bool containerSkipped;
+    LayoutObject* o = container(paintInvalidationContainer, &containerSkipped);
     if (!o)
         return;
 
-    // FIXME: this should call offsetFromContainer to share code, but I'm not sure it's ever called.
-    LayoutPoint centerPoint = roundedLayoutPoint(transformState.mappedPoint());
-    if (mode & ApplyContainerFlip && o->isBox()) {
-        if (o->style()->isFlippedBlocksWritingMode())
-            transformState.move(toLayoutBox(o)->flipForWritingMode(roundedLayoutPoint(transformState.mappedPoint())) - centerPoint);
+    if (isBox()) {
+        bool isFixedPos = style()->position() == FixedPosition;
+        bool hasTransform = hasLayer() && toLayoutBox(this)->layer()->transform();
+        // If this box has a transform, it acts as a fixed position container for fixed descendants,
+        // and may itself also be fixed position. So propagate 'fixed' up only if this box is fixed position.
+        if (hasTransform && !isFixedPos)
+            mode &= ~IsFixed;
+        else if (isFixedPos)
+            mode |= IsFixed;
+
+        if (wasFixed)
+            *wasFixed = mode & IsFixed;
+
+        mode &= ~ApplyContainerFlip;
+        paintInvalidationState = nullptr;
+    } else if (mode & ApplyContainerFlip && o->isBox()) {
+        if (o->style()->isFlippedBlocksWritingMode()) {
+            IntPoint centerPoint = roundedIntPoint(transformState.mappedPoint());
+            transformState.move(toLayoutBox(o)->flipForWritingMode(LayoutPoint(centerPoint)) - centerPoint);
+        }
         mode &= ~ApplyContainerFlip;
     }
 
-    transformState.move(o->columnOffset(roundedLayoutPoint(transformState.mappedPoint())));
+    LayoutSize containerOffset = offsetFromContainer(o);
+    containerOffset += o->columnOffset(roundedLayoutPoint(transformState.mappedPoint()) + containerOffset);
 
-    if (o->hasOverflowClip())
-        transformState.move(-toLayoutBox(o)->scrolledContentOffset());
+    bool preserve3D = mode & UseTransforms && (o->style()->preserves3D() || (!isText() && style()->preserves3D()));
+    if (mode & UseTransforms && shouldUseTransformFromContainer(o)) {
+        TransformationMatrix t;
+        getTransformFromContainer(o, containerOffset, t);
+        transformState.applyTransform(t, preserve3D ? TransformState::AccumulateTransform : TransformState::FlattenTransform);
+    } else {
+        transformState.move(containerOffset.width(), containerOffset.height(), preserve3D ? TransformState::AccumulateTransform : TransformState::FlattenTransform);
+    }
+
+    if (containerSkipped) {
+        // There can't be a transform between paintInvalidationContainer and o, because transforms create containers, so it should be safe
+        // to just subtract the delta between the paintInvalidationContainer and o.
+        LayoutSize containerOffset = paintInvalidationContainer->offsetFromAncestorContainer(o);
+        transformState.move(-containerOffset.width(), -containerOffset.height(), preserve3D ? TransformState::AccumulateTransform : TransformState::FlattenTransform);
+        return;
+    }
 
     o->mapLocalToContainer(paintInvalidationContainer, transformState, mode, wasFixed, paintInvalidationState);
 }
@@ -2107,8 +2148,8 @@ void LayoutObject::getTransformFromContainer(const LayoutObject* containerObject
 
 FloatQuad LayoutObject::localToContainerQuad(const FloatQuad& localQuad, const LayoutBoxModelObject* paintInvalidationContainer, MapCoordinatesFlags mode, bool* wasFixed) const
 {
-    // Track the point at the center of the quad's bounding box. As mapLocalToContainer() calls offsetFromContainer(),
-    // it will use that point as the reference point to decide which column's transform to apply in multiple-column blocks.
+    // Track the point at the center of the quad's bounding box. mapLocalToContainer() will use
+    // that point as the reference point to decide which column we're in for multiple-column blocks.
     TransformState transformState(TransformState::ApplyTransformDirection, localQuad.boundingBox().center(), localQuad);
     mapLocalToContainer(paintInvalidationContainer, transformState, mode | ApplyContainerFlip | UseTransforms, wasFixed);
     transformState.flatten();
@@ -2143,19 +2184,12 @@ FloatPoint LayoutObject::localToInvalidationBackingPoint(const LayoutPoint& loca
     return containerPoint;
 }
 
-LayoutSize LayoutObject::offsetFromContainer(const LayoutObject* o, const LayoutPoint& point, bool* offsetDependsOnPoint) const
+LayoutSize LayoutObject::offsetFromContainer(const LayoutObject* o) const
 {
     ASSERT(o == container());
-
-    LayoutSize offset = o->columnOffset(point);
-
     if (o->hasOverflowClip())
-        offset -= toLayoutBox(o)->scrolledContentOffset();
-
-    if (offsetDependsOnPoint)
-        *offsetDependsOnPoint = o->isLayoutFlowThread();
-
-    return offset;
+        return LayoutSize(-toLayoutBox(o)->scrolledContentOffset());
+    return LayoutSize();
 }
 
 LayoutSize LayoutObject::offsetFromAncestorContainer(const LayoutObject* container) const
@@ -2172,7 +2206,8 @@ LayoutSize LayoutObject::offsetFromAncestorContainer(const LayoutObject* contain
         if (!nextContainer)
             break;
         ASSERT(!currContainer->hasTransformRelatedProperty());
-        LayoutSize currentOffset = currContainer->offsetFromContainer(nextContainer, referencePoint);
+        LayoutSize currentOffset = currContainer->offsetFromContainer(nextContainer);
+        currentOffset += container->columnOffset(referencePoint + currentOffset);
         offset += currentOffset;
         referencePoint.move(currentOffset);
         currContainer = nextContainer;