Update check for cyclic typedefs.

sdk/lib/_internal/compiler/implementation/elements/modelx.dart

Index: sdk/lib/_internal/compiler/implementation/elements/modelx.dart
diff --git a/sdk/lib/_internal/compiler/implementation/elements/modelx.dart b/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
index fccf1bff5dd05c409fdc765f129c7d63055dc9c1..c2234a4dc64fb57220a86198da320826ab9d5af0 100644
--- a/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
+++ b/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
@@ -995,6 +995,9 @@ class TypedefElementX extends ElementX implements TypedefElement {
    */
   DartType alias;
 
+  /// [:true:] if the typedef has been checked for cyclic reference.
+  bool hasBeenCheckedForCycles = false;
+
   bool get isResolved => mapping != null;
 
   // TODO(johnniwinther): Store the mapping in the resolution enqueuer instead.
@@ -1038,6 +1041,13 @@ class TypedefElementX extends ElementX implements TypedefElement {
   Scope buildScope() {
     return new TypeDeclarationScope(enclosingElement.buildScope(), this);
   }
+
+  void checkCyclicReference(Compiler compiler) {
+    if (hasBeenCheckedForCycles) return;
+    var visitor = new TypedefCyclicVisitor(compiler, this);
+    computeType(compiler).accept(visitor, null);
+    hasBeenCheckedForCycles = true;
+  }
 }
 
 class VariableElementX extends ElementX implements VariableElement {