ancestorOverflowLayer should not cross frame boundaries.

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

Index: third_party/WebKit/Source/core/paint/PrePaintTreeWalk.cpp
diff --git a/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.cpp b/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.cpp
index 9eb113c271eb2b5925b3f1b47ab2827c34e0d924..d0525b5f71259013829ab8e852806d7902f4eabe 100644
--- a/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.cpp
+++ b/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.cpp
@@ -53,6 +53,8 @@ bool PrePaintTreeWalk::walk(FrameView& frameView,
   }
 
   PrePaintTreeWalkContext context(parentContext);
+  // ancestorOverflowLayer does not cross frame boundaries.
+  context.ancestorOverflowPaintLayer = nullptr;
   m_propertyTreeBuilder.updateProperties(frameView, context.treeBuilderContext);
   m_paintInvalidator.invalidatePaintIfNeeded(frameView,
                                              context.paintInvalidatorContext);