Ensure that we consistently check contains: paint for fixed position containment.

third_party/WebKit/Source/core/layout/LayoutBox.cpp

Index: third_party/WebKit/Source/core/layout/LayoutBox.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBox.cpp b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
index 4a8c20e3dea1bc54408e7779dd067fe549010a9d..681374d984ae9a33d8fa017e12bdc7b534958fdf 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -1728,10 +1728,10 @@ LayoutUnit LayoutBox::perpendicularContainingBlockLogicalHeight() const
 void LayoutBox::mapLocalToAncestor(const LayoutBoxModelObject* ancestor, TransformState& transformState, MapCoordinatesFlags mode) const
 {
     bool isFixedPos = style()->position() == FixedPosition;
-    bool hasTransform = hasLayer() && layer()->transform();
-    // If this box has a transform, it acts as a fixed position container for fixed descendants,
+
+    // If this box has a transform or contains paint, 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)
+    if (style()->canContainFixedPositionObjects() && !isFixedPos)
         mode &= ~IsFixed;
     else if (isFixedPos)
         mode |= IsFixed;
@@ -1745,9 +1745,9 @@ void LayoutBox::mapAncestorToLocal(const LayoutBoxModelObject* ancestor, Transfo
         return;
 
     bool isFixedPos = style()->position() == FixedPosition;
-    bool hasTransform = hasLayer() && layer()->transform();
-    if (hasTransform && !isFixedPos) {
-        // If this box has a transform, it acts as a fixed position container for fixed descendants,
+
+    if (style()->canContainFixedPositionObjects() && !isFixedPos) {
+        // If this box has a transform or contains paint, 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.
         mode &= ~IsFixed;
     } else if (isFixedPos) {