Resynthesize mixins from Kernel.

pkg/kernel/lib/binary/ast_to_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_to_binary;
 
 import '../ast.dart';
 import '../import_table.dart';
 import 'tag.dart';
 import 'dart:convert';
 import 'dart:typed_data';
@@ skipping 345 matching lines @@
 
   void writeAnnotation(Expression annotation) {
     _variableIndexer ??= new VariableIndexer();
     writeNode(annotation);
   }
 
   void writeAnnotationList(List<Expression> annotations) {
     writeList(annotations, writeAnnotation);
   }
 
-  int _encodeClassFlags(bool isAbstract, ClassLevel level) {
-    int abstactFlag = isAbstract ? 1 : 0;
-    int levelFlags = (level.index - 1) << 1;
-    return abstactFlag | levelFlags;
+  int _encodeClassFlags(
+      bool isAbstract, bool isSyntheticMixinImplementation, ClassLevel level) {
+    int abstractFlag = isAbstract ? 1 : 0;
+    int isSyntheticMixinImplementationFlag =
+        isSyntheticMixinImplementation ? 2 : 0;
+    int levelFlags = (level.index - 1) << 2;
+    return abstractFlag | isSyntheticMixinImplementationFlag | levelFlags;
   }
 
   visitClass(Class node) {
-    int flags = _encodeClassFlags(node.isAbstract, node.level);
+    int flags = _encodeClassFlags(
+        node.isAbstract, node.isSyntheticMixinImplementation, node.level);
     if (node.canonicalName == null) {
       throw 'Missing canonical name for $node';
     }
     node.binaryOffset = _sink.flushedLength + _sink.length;
     writeByte(Tag.Class);
     writeCanonicalNameReference(getCanonicalNameOfClass(node));
     writeOffset(node.fileOffset);
     writeOffset(node.fileEndOffset);
     writeByte(flags);
     writeStringReference(node.name ?? '');
@@ skipping 1121 matching lines @@
     _sink.add(_buffer.sublist(0, length));
     _buffer = new Uint8List(SIZE);
     flushedLength += length;
     length = 0;
   }
 
   void flushAndDestroy() {
     _sink.add(_buffer.sublist(0, length));
   }
 }