Add --modules=node support

lib/runtime/dart/_interceptors.js

 dart_library.library('dart/_interceptors', null, /* Imports */[
   'dart/_runtime',
   'dart/core',
   'dart/_internal',
   'dart/collection',
   'dart/math'
 ], /* Lazy imports */[
   'dart/_js_helper'
 ], function(exports, dart, core, _internal, collection, math, _js_helper) {
   'use strict';
@@ skipping 410 matching lines @@
         [dartx.get]: [E, [core.int]],
         [dartx.set]: [dart.void, [core.int, E]],
         [dartx.asMap]: [core.Map$(core.int, E), []]
       }),
       statics: () => ({markFixedList: [core.List, [core.List]]}),
       names: ['markFixedList']
     });
     JSArray[dart.metadata] = () => [dart.const(new _js_helper.JsPeerInterface({name: 'Array'}))];
     return JSArray;
   });
-  let JSArray = JSArray$();
+  const JSArray = JSArray$();
   dart.registerExtension(dart.global.Array, JSArray);
   const JSMutableArray$ = dart.generic(function(E) {
     class JSMutableArray extends JSArray$(E) {
       JSMutableArray() {
         super.JSArray();
       }
     }
     JSMutableArray[dart.implements] = () => [JSMutableIndexable];
     return JSMutableArray;
   });
-  let JSMutableArray = JSMutableArray$();
+  const JSMutableArray = JSMutableArray$();
   const JSFixedArray$ = dart.generic(function(E) {
     class JSFixedArray extends JSMutableArray$(E) {}
     return JSFixedArray;
   });
-  let JSFixedArray = JSFixedArray$();
+  const JSFixedArray = JSFixedArray$();
   const JSExtendableArray$ = dart.generic(function(E) {
     class JSExtendableArray extends JSMutableArray$(E) {}
     return JSExtendableArray;
   });
-  let JSExtendableArray = JSExtendableArray$();
+  const JSExtendableArray = JSExtendableArray$();
   class Interceptor extends core.Object {
     Interceptor() {
     }
   }
   dart.setSignature(Interceptor, {
     constructors: () => ({Interceptor: [Interceptor, []]})
   });
   const _isInt32 = Symbol('_isInt32');
   const _tdivSlow = Symbol('_tdivSlow');
   const _shlPositive = Symbol('_shlPositive');
@@ skipping 958 matching lines @@
   exports.JSString = JSString;
   exports.getInterceptor = getInterceptor;
   exports.JSBool = JSBool;
   exports.JSIndexable = JSIndexable;
   exports.JSMutableIndexable = JSMutableIndexable;
   exports.JSObject = JSObject;
   exports.JavaScriptObject = JavaScriptObject;
   exports.PlainJavaScriptObject = PlainJavaScriptObject;
   exports.UnknownJavaScriptObject = UnknownJavaScriptObject;
 });