Implement Paint Containment

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

Index: third_party/WebKit/Source/core/paint/PaintLayer.h
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.h b/third_party/WebKit/Source/core/paint/PaintLayer.h
index ccb457742376b6f94f3383fbf753d21ff1483e1b..eda95c5359342ef60c55dd8a563187b4ef3d7c71 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.h
@@ -266,7 +266,7 @@ public:
     // the ancestry chain between this layer and the containing block layer; if not found, it will
     // be set to false. Either both |ancestor| and |skippedAncestor| should be nullptr, or none of
     // them should.
-    PaintLayer* enclosingPositionedAncestor(const PaintLayer* ancestor = nullptr, bool* skippedAncestor = nullptr) const;
+    PaintLayer* enclosingPositionedOrContainedAncestor(const PaintLayer* ancestor = nullptr, bool* skippedAncestor = nullptr) const;
 
     bool isPaintInvalidationContainer() const;
 
@@ -463,7 +463,7 @@ public:
         // LayoutObject::canContainFixedPositionObjects() should probably be used
         // instead.
         LayoutBoxModelObject* layerlayoutObject = layoutObject();
-        return isRootLayer() || layerlayoutObject->isPositioned() || hasTransformRelatedProperty();
+        return isRootLayer() || layerlayoutObject->isPositioned() || hasTransformRelatedProperty() || layerlayoutObject->style()->containsPaint();

[chrishtr, 2015/12/09 01:41:46]

It's not really positioned..

[leviw_travelin_and_unemployed, 2015/12/09 21:09:24]

That's because this method and its one caller, despite the name, aren't really
looking for a positioned container, they're looking for the container for a
positioned items. I'm not a fan of this code being here to begin with, honestly.

     }
 
     bool scrollsOverflow() const;