Ensure supertypes are loaded safely.

dart/lib/compiler/implementation/ssa/closure.dart

 // Copyright (c) 2012, 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 ClosureFieldElement extends Element {
   ClosureFieldElement(SourceString name, ClassElement enclosing)
       : super(name, ElementKind.FIELD, enclosing);
 
   bool isInstanceMember() => true;
   bool isAssignable() => false;
 
   String toString() => "ClosureFieldElement($name)";
 }
 
 class ClosureClassElement extends ClassElement {
   ClosureClassElement(SourceString name,
                       Compiler compiler,
                       Element enclosingElement)
       : super(name,
               enclosingElement,
               // By assigning a fresh class-id we make sure that the hashcode
               // is unique, but also emit closure classes after all other
               // classes (since the emitter sorts classes by their id).
               compiler.getNextFreeClassId()) {
-    isResolved = true;
+    // We assign twice to [supertypeLoadState] as it contains asserts
+    // which enforce certain sequence of transitions.
+    supertypeLoadState = ClassElement.STATE_STARTED;
+    supertypeLoadState = ClassElement.STATE_DONE;
+    // Same as for [supertypeLoadState] above.
+    resolutionState = ClassElement.STATE_STARTED;
+    resolutionState = ClassElement.STATE_DONE;
     compiler.closureClass.ensureResolved(compiler);
     supertype = compiler.closureClass.computeType(compiler);
+    interfaces = const EmptyLink<Type>();
   }
   bool isClosure() => true;
 }
 
 class BoxElement extends Element {
   BoxElement(SourceString name, Element enclosingElement)
       : super(name, ElementKind.VARIABLE, enclosingElement);
 }
 
 class ThisElement extends Element {
@@ skipping 426 matching lines @@
   }
 
   visitTryStatement(TryStatement node) {
     // TODO(ngeoffray): implement finer grain state.
     bool oldInTryStatement = inTryStatement;
     inTryStatement = true;
     node.visitChildren(this);
     inTryStatement = oldInTryStatement;
   }
 }