Ensure supertypes are loaded safely.

dart/lib/compiler/implementation/scanner/class_element_parser.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class ClassElementParser extends PartialParser {
   ClassElementParser(Listener listener) : super(listener);
 
   Token parseClassBody(Token token) => fullParseClassBody(token);
 }
 
@@ skipping 19 matching lines @@
     assert(listener.nodes.isEmpty());
     return cachedNode;
   }
 
   Token position() => beginToken;
 
   bool isInterface() => beginToken.stringValue === "interface";
 
   PartialClassElement cloneTo(Element enclosing, DiagnosticListener listener) {
     parseNode(listener);
+    // TODO(lrn): Is copying id acceptable?
+    // TODO(ahe): No.
     PartialClassElement result =
         new PartialClassElement(name, beginToken, endToken, enclosing, id);
-    cloneMembersTo(result, listener);
+
+    assert(this.supertypeLoadState == ClassElement.STATE_NOT_STARTED);
+    assert(this.resolutionState == ClassElement.STATE_NOT_STARTED);
+    assert(this.type === null);
+    assert(this.supertype === null);
+    assert(this.defaultClass === null);
+    assert(this.interfaces === null);
+    assert(this.allSupertypes === null);
+    assert(this.backendMembers.isEmpty());
+
+    // Native is only used in DOM/HTML library for which we don't
+    // support patching.
+    assert(this.nativeName === null);
+
+    Link<Element> elementList = this.members;
+    while (!elementList.isEmpty()) {
+      result.addMember(elementList.head.cloneTo(result, listener), listener);
+      elementList = elementList.tail;
+    }
+
     result.cachedNode = cachedNode;
     return result;
   }
 }
 
 class MemberListener extends NodeListener {
   final ClassElement enclosingElement;
 
   MemberListener(DiagnosticListener listener,
                  Element enclosingElement)
@@ skipping 85 matching lines @@
   }
 
   void endInitializers(int count, Token beginToken, Token endToken) {
     pushNode(null);
   }
 
   void addMember(Element memberElement) {
     enclosingElement.addMember(memberElement, listener);
   }
 }