Add Class.isEnum to Kernel and use it to resynthesize enums in Analyzer.

pkg/kernel/lib/ast.dart

 // Copyright (c) 2016, 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.
 
 /// -----------------------------------------------------------------------
 ///                           ERROR HANDLING
 /// -----------------------------------------------------------------------
 ///
 /// As a rule of thumb, errors that can be detected statically are handled by
 /// the frontend, typically by translating the erroneous code into a 'throw' or
@@ skipping 598 matching lines @@
   /// Name of the class.
   ///
   /// Must be non-null and must be unique within the library.
   ///
   /// The name may contain characters that are not valid in a Dart identifier,
   /// in particular, the symbol '&' is used in class names generated for mixin
   /// applications.
   String name;
   bool isAbstract;
 
+  /// Whether this class is an enum.
+  @informative
+  bool isEnum = false;
+
   /// Whether this class is a synthetic implementation created for each
   /// mixed-in class. For example the following code:
   /// class Z extends A with B, C, D {}
   /// class A {}
   /// class B {}
   /// class C {}
   /// class D {}
   /// ...creates:
   /// abstract class A&B extends A mixedIn B {}
   /// abstract class A&B&C extends A&B mixedIn C {}
@@ skipping 4051 matching lines @@
   if (typedef_.canonicalName == null) {
     throw '$typedef_ has no canonical name';
   }
   return typedef_.canonicalName;
 }
 
 /// Annotation describing information which is not part of Dart semantics; in
 /// other words, if this information (or any information it refers to) changes,
 /// static analysis and runtime behavior of the library are unaffected.
 const informative = null;