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

pkg/kernel/lib/binary/ast_from_binary.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.
 library kernel.ast_from_binary;
 
 import 'dart:convert';
 import 'dart:typed_data';
 
 import '../ast.dart';
 import '../transformations/flags.dart';
@@ skipping 445 matching lines @@
     var reference = canonicalName.getReference();
     Class node = reference.node;
     bool shouldWriteData = node == null || _isReadingLibraryImplementation;
     if (node == null) {
       node = new Class(reference: reference)..level = ClassLevel.Temporary;
     }
     node.fileOffset = readOffset();
     node.fileEndOffset = readOffset();
     int flags = readByte();
     node.isAbstract = flags & 0x1 != 0;
-    node.isSyntheticMixinImplementation = flags & 0x2 != 0;
-    int levelIndex = (flags >> 2) & 0x3;
+    node.isEnum = flags & 0x2 != 0;
+    node.isSyntheticMixinImplementation = flags & 0x4 != 0;
+    int levelIndex = (flags >> 3) & 0x3;
     var level = ClassLevel.values[levelIndex + 1];
     if (level.index >= node.level.index) {
       node.level = level;
     }
     var name = readStringOrNullIfEmpty();
     var fileUri = readUriReference();
     var documentationComment = readStringOrNullIfEmpty();
     var annotations = readAnnotationList(node);
     debugPath.add(node.name ?? 'normal-class');
     readAndPushTypeParameterList(node.typeParameters, node);
@@ skipping 776 matching lines @@
       ..fileOffset = offset
       ..fileEqualsOffset = fileEqualsOffset;
   }
 
   int readOffset() {
     // Offset is saved as unsigned,
     // but actually ranges from -1 and up (thus the -1)
     return readUInt() - 1;
   }
 }