partially implement instance of checks and some codegen fixes

lib/src/js/nodes.dart

 // Copyright (c) 2012, 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.
 
 part of js_ast;
 
 abstract class NodeVisitor<T> {
   T visitProgram(Program node);
 
   T visitBlock(Block node);
@@ skipping 695 matching lines @@
 
   int get precedenceLevel => CALL;
 }
 
 class New extends Call {
   New(Expression cls, List<Expression> arguments) : super(cls, arguments);
 
   accept(NodeVisitor visitor) => visitor.visitNew(this);
 
   New _clone() => new New(target, arguments);
+
+  int get precedenceLevel => ACCESS;
 }
 
 class Binary extends Expression {
   final String op;
   final Expression left;
   final Expression right;
 
   Binary(this.op, this.left, this.right);
 
   accept(NodeVisitor visitor) => visitor.visitBinary(this);
@@ skipping 215 matching lines @@
 
   accept(NodeVisitor visitor) => visitor.visitAccess(this);
 
   void visitChildren(NodeVisitor visitor) {
     receiver.accept(visitor);
     selector.accept(visitor);
   }
 
   PropertyAccess _clone() => new PropertyAccess(receiver, selector);
 
-  int get precedenceLevel => CALL;
+  int get precedenceLevel => ACCESS;
 }
 
 abstract class Literal extends Expression {
   void visitChildren(NodeVisitor visitor) {}
 
   int get precedenceLevel => PRIMARY;
 }
 
 class LiteralBool extends Literal {
   final bool value;
@@ skipping 378 matching lines @@
   final Expression expression;
 
   CommentExpression(this.comment, this.expression);
 
   int get precedenceLevel => PRIMARY;
   accept(NodeVisitor visitor) => visitor.visitCommentExpression(this);
   CommentExpression _clone() => new CommentExpression(comment, expression);
 
   void visitChildren(NodeVisitor visitor) => expression.accept(visitor);
 }