Strictly unbreakable objects need to prevent interaction with the outside.

third_party/WebKit/Source/core/layout/LayoutMultiColumnFlowThread.h

Index: third_party/WebKit/Source/core/layout/LayoutMultiColumnFlowThread.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutMultiColumnFlowThread.h b/third_party/WebKit/Source/core/layout/LayoutMultiColumnFlowThread.h
index 91fb0d701095c9232c04cb2d6a73b1d25d17f229..457b97eb73e17a3f7194cb5854ee0fbe336592bd 100644
--- a/third_party/WebKit/Source/core/layout/LayoutMultiColumnFlowThread.h
+++ b/third_party/WebKit/Source/core/layout/LayoutMultiColumnFlowThread.h
@@ -260,21 +260,8 @@ class CORE_EXPORT LayoutMultiColumnFlowThread : public LayoutFlowThread,
   bool removeSpannerPlaceholderIfNoLongerValid(
       LayoutBox* spannerObjectInFlowThread);
 
-  // Search mode when looking for an enclosing fragmentation context.
-  enum AncestorSearchConstraint {
-    // No constraints. Sometimes we just want to find all enclosing
-    // fragmentation contexts, e.g. to calculate the accumulated visual
-    // translation.
-    AnyAncestor,
-
-    // Consider fragmentation contexts that are strictly unbreakable (seen from
-    // the outside) to be isolated from the rest, so that such fragmentation
-    // contexts don't participate in fragmentation of enclosing fragmentation
-    // contexts, apart from taking up space and otherwise being completely
-    // unbreakable. This is typically what we want to do during layout.
-    IsolateUnbreakableContainers,
-  };
-  LayoutMultiColumnFlowThread* enclosingFlowThread() const;
+  LayoutMultiColumnFlowThread* enclosingFlowThread(
+      AncestorSearchConstraint = IsolateUnbreakableContainers) const;
   FragmentationContext* enclosingFragmentationContext(
       AncestorSearchConstraint = IsolateUnbreakableContainers) const;
   LayoutUnit blockOffsetInEnclosingFragmentationContext() const {