Fix a corner case of constant constructor dependency computation.

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 439 matching lines @@
         initializer.accept(referenceFinder);
       }
       if (!superInvocationFound) {
         // No explicit superconstructor invocation found, so we need to
         // manually insert a reference to the implicit superconstructor.
         InterfaceType superclass =
             (constant.returnType as InterfaceType).superclass;
         if (superclass != null && !superclass.isObject) {
           ConstructorElement unnamedConstructor = ConstantEvaluationEngine
               ._getConstructorBase(superclass.element.unnamedConstructor);
-          if (unnamedConstructor != null) {
+          if (unnamedConstructor != null && unnamedConstructor.isConst) {
             callback(unnamedConstructor);
           }
         }
       }
       for (FieldElement field in constant.enclosingElement.fields) {
         // Note: non-static const isn't allowed but we handle it anyway so that
         // we won't be confused by incorrect code.
         if ((field.isFinal || field.isConst) &&
             !field.isStatic &&
             field.initializer != null) {
@@ skipping 4749 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;
 }