Avoid infinite loop if const constructor redirects don't reach a fixed point.

pkg/analyzer/lib/src/generated/constant.dart

 // Copyright (c) 2014, 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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.constant;
 
 import 'dart:collection';
@@ skipping 977 matching lines @@
     while (constructor.isFactory) {
       if (identical(
           constructor.enclosingElement.type, typeProvider.symbolType)) {
         // The dart:core.Symbol has a const factory constructor that redirects
         // to dart:_internal.Symbol.  That in turn redirects to an external
         // const constructor, which we won't be able to evaluate.
         // So stop following the chain of redirections at dart:core.Symbol, and
         // let [evaluateInstanceCreationExpression] handle it specially.
         break;
       }
-      constructorsVisited.add(constructor);
+      ConstructorElement constructorBase = _getConstructorBase(constructor);
+      constructorsVisited.add(constructorBase);
       ConstructorElement redirectedConstructor =
           constructor.redirectedConstructor;
       if (redirectedConstructor == null) {
         // This can happen if constructor is an external factory constructor.
         break;
       }
       if (!redirectedConstructor.isConst) {
         // Delegating to a non-const constructor--this is not allowed (and
         // is checked elsewhere--see
         // [ErrorVerifier.checkForRedirectToNonConstConstructor()]).
         break;
       }
-      if (constructorsVisited.contains(redirectedConstructor)) {
+      ConstructorElement redirectedConstructorBase =
+          _getConstructorBase(redirectedConstructor);
+      if (constructorsVisited.contains(redirectedConstructorBase)) {
         // Cycle in redirecting factory constructors--this is not allowed
         // and is checked elsewhere--see
         // [ErrorVerifier.checkForRecursiveFactoryRedirect()]).
         break;
       }
       constructor = redirectedConstructor;
     }
     return constructor;
   }
 
@@ skipping 4040 matching lines @@
       return BoolState.from(_element == rightElement);
     } else if (rightOperand is DynamicState) {
       return BoolState.UNKNOWN_VALUE;
     }
     return BoolState.FALSE_STATE;
   }
 
   @override
   String toString() => _element == null ? "-unknown-" : _element.name;
 }