Disallow off-heap containers containing raw on-heap pointers.

third_party/WebKit/Source/wtf/LinkedHashSet.h

Index: third_party/WebKit/Source/wtf/LinkedHashSet.h
diff --git a/third_party/WebKit/Source/wtf/LinkedHashSet.h b/third_party/WebKit/Source/wtf/LinkedHashSet.h
index 65f5100a8f133fa66fb81d123c1a0c710d546375..0a2235a0eeb054af291152ea363a058e78dce483 100644
--- a/third_party/WebKit/Source/wtf/LinkedHashSet.h
+++ b/third_party/WebKit/Source/wtf/LinkedHashSet.h
@@ -598,8 +598,14 @@ class LinkedHashSetConstReverseIterator
   friend class LinkedHashSet;
 };
 
-template <typename T, typename U, typename V, typename W>
-inline LinkedHashSet<T, U, V, W>::LinkedHashSet() {}
+template <typename T, typename U, typename V, typename Allocator>
+inline LinkedHashSet<T, U, V, Allocator>::LinkedHashSet() {
+  static_assert(
+      Allocator::isGarbageCollected ||
+          !IsPointerToGarbageCollectedType<T>::value,
+      "Cannot put raw pointers to garbage-collected classes into "
+      "an off-heap LinkedHashSet. Use HeapLinkedHashSet<Member<T>> instead.");
+}
 
 template <typename T, typename U, typename V, typename W>
 inline LinkedHashSet<T, U, V, W>::LinkedHashSet(const LinkedHashSet& other)