Ensure supertypes are loaded safely.

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

Index: dart/lib/compiler/implementation/ssa/closure.dart
diff --git a/dart/lib/compiler/implementation/ssa/closure.dart b/dart/lib/compiler/implementation/ssa/closure.dart
index f6f0e3da4b48afc2d79568715998960f1d10fbca..a3a11d4d82876c06db24cf9d84ad49b488e1de5e 100644
--- a/dart/lib/compiler/implementation/ssa/closure.dart
+++ b/dart/lib/compiler/implementation/ssa/closure.dart
@@ -22,9 +22,16 @@ class ClosureClassElement extends ClassElement {
               // 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;
 }