compute interfaces lazily

lib/src/codegen/js_codegen.dart

 // Copyright (c) 2015, 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 dev_compiler.src.codegen.js_codegen;
 
 import 'dart:collection' show HashSet, HashMap;
 import 'dart:io' show Directory, File;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
@@ skipping 536 matching lines @@
   JS.Statement _finishClassMembers(ClassElement classElem,
       JS.ClassExpression cls, List<ConstructorDeclaration> ctors,
       List<FieldDeclaration> staticFields) {
     var name = classElem.name;
 
     var body = <JS.Statement>[];
     body.add(new JS.ClassDeclaration(cls));
 
     // Interfaces
     if (classElem.interfaces.isNotEmpty) {
-      body.add(js.statement('#[dart.implements] = #;', [
+      body.add(js.statement('#[dart.implements] = () => #;', [
         name,
         new JS.ArrayInitializer(
             classElem.interfaces.map(_emitTypeName).toList())
       ]));
     }
 
     // Named constructors
     for (ConstructorDeclaration member in ctors) {
       if (member.name != null) {
         body.add(js.statement('dart.defineNamedConstructor(#, #);', [
@@ skipping 1810 matching lines @@
 
     // TODO(jmesserly): in many cases marking the end will be unncessary.
     printer.mark(_location(node.end));
   }
 
   String _getIdentifier(AstNode node) {
     if (node is SimpleIdentifier) return node.name;
     return null;
   }
 }