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

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

Index: third_party/WebKit/Source/core/paint/PaintLayer.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.cpp b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
index 663bafd43d606dc22b1d77cb28b354bb405d56df..24e53f6be10979f106bfa302bafaebb55304fdb0 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -846,20 +846,6 @@ FloatPoint PaintLayer::perspectiveOrigin() const
     return FloatPoint(floatValueForLength(style.perspectiveOriginX(), borderBox.width().toFloat()), floatValueForLength(style.perspectiveOriginY(), borderBox.height().toFloat()));
 }
 
-static inline bool isContainerForFixedPositioned(PaintLayer* layer)

[flackr, 2016/07/22 18:28:30]

Seems like these methods are just asking to get out of sync with LayoutObject's
methods. How about we try just calling into layoutObject, especially considering
we need to to check both fixed and positioned now anyways?

-{
-    return layer->isRootLayer() || layer->hasTransformRelatedProperty();
-}
-
-static inline bool isContainerForPositioned(PaintLayer* layer)
-{
-    // FIXME: This is not in sync with containingBlock.
-    // LayoutObject::canContainFixedPositionObjects() should probably be used
-    // instead.
-    LayoutBoxModelObject* layerlayoutObject = layer->layoutObject();
-    return layer->isRootLayer() || layerlayoutObject->isPositioned() || layer->hasTransformRelatedProperty() || layerlayoutObject->style()->containsPaint();
-}
-
 PaintLayer* PaintLayer::containingLayerForOutOfFlowPositioned(const PaintLayer* ancestor, bool* skippedAncestor) const
 {
     ASSERT(!ancestor || skippedAncestor); // If we have specified an ancestor, surely the caller needs to know whether we skipped it.
@@ -867,7 +853,7 @@ PaintLayer* PaintLayer::containingLayerForOutOfFlowPositioned(const PaintLayer*
         *skippedAncestor = false;
     if (layoutObject()->style()->position() == FixedPosition) {
         PaintLayer* curr = parent();
-        while (curr && !isContainerForFixedPositioned(curr)) {
+        while (curr && !curr->layoutObject()->canContainFixedPositionObjects()) {
             if (skippedAncestor && curr == ancestor)
                 *skippedAncestor = true;
             curr = curr->parent();
@@ -877,7 +863,7 @@ PaintLayer* PaintLayer::containingLayerForOutOfFlowPositioned(const PaintLayer*
     }
 
     PaintLayer* curr = parent();
-    while (curr && !isContainerForPositioned(curr)) {
+    while (curr && !curr->layoutObject()->canContainAbsolutePositionObjects()) {
         if (skippedAncestor && curr == ancestor)
             *skippedAncestor = true;
         curr = curr->parent();