Add missing visit methods

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 277 matching lines @@
 
     var classExpr = new JS.ClassExpression(new JS.VariableDeclaration(name),
         _classHeritage(node), _emitClassMethods(node, ctors, fields));
 
     var body = _finishClassMembers(name, classExpr, ctors, staticFields);
     currentClass = null;
 
     return _finishClassDef(classElem, body);
   }
 
+  @override
+  JS.Statement visitEnumDeclaration(EnumDeclaration node) =>
+      _unimplementedCall("Unimplemented enum: $node").toStatement();
+
   /// Given a class element and body, complete the class declaration.
   /// This handles generic type parameters, laziness (in library-cycle cases),
   /// and ensuring dependencies are loaded first.
   JS.Statement _finishClassDef(ClassElement classElem, JS.Statement body) {
     var name = classElem.name;
     var genericName = '$name\$';
 
     JS.Statement genericDef;
     JS.Expression genericInst;
     if (classElem.typeParameters.isNotEmpty) {
@@ skipping 1641 matching lines @@
   visitInterpolationExpression(InterpolationExpression node) =>
       _visit(node.expression);
 
   @override
   visitBooleanLiteral(BooleanLiteral node) => js.boolean(node.value);
 
   @override
   JS.Expression visitExpression(Expression node) =>
       _unimplementedCall('Unimplemented ${node.runtimeType}: $node');
 
+  @override
+  JS.Statement visitYieldStatement(YieldStatement node) =>
+      _unimplementedCall('Unimplemented yield: $node').toStatement();
+
   JS.Expression _unimplementedCall(String comment) {
     return js.call('dart.throw_(#)', [js.escapedString(comment)]);
   }
 
   @override
   visitNode(AstNode node) {
     // TODO(jmesserly): verify this is unreachable.
     throw 'Unimplemented ${node.runtimeType}: $node';
   }
 
@@ skipping 331 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;
   }
 }