First cut of mini dart:html.

lib/runtime/dart/js.js

 dart_library.library('dart/js', null, /* Imports */[
   "dart/_runtime",
   'dart/core',
   'dart/collection',
   'dart/_js_helper'
 ], /* Lazy imports */[
 ], function(exports, dart, core, collection, _js_helper) {
   'use strict';
   let dartx = dart.dartx;
+  const _global = dart.global;
   dart.defineLazyProperties(exports, {
     get context() {
-      return _wrapToDart(dart.global);
+      return _wrapToDart(_global);
     }
   });
   const _jsObject = Symbol('_jsObject');
   class JsObject extends core.Object {
     _fromJs(jsObject) {
       this[_jsObject] = jsObject;
       dart.assert(this[_jsObject] != null);
     }
     static new(constructor, arguments$) {
       if (arguments$ === void 0)
@@ skipping 320 matching lines @@
   dart.fn(_convertToJS);
   function _wrapDartFunction(f) {
     let wrapper = function() {
       let args = Array.prototype.map.call(arguments, _convertToDart);
       return _convertToJS(f(...args));
     };
     dart.dsetindex(_dartProxies, wrapper, f);
     return wrapper;
   }
   dart.fn(_wrapDartFunction);
-  function _convertToDart(o) {
-    if (o == null || typeof o == "string" || typeof o == "number" || typeof o == "boolean" || dart.notNull(_isBrowserType(o))) {
+  function _convertToDart(o, isBrowserType) {
+    if (isBrowserType === void 0)
+      isBrowserType = null;
+    if (isBrowserType == null)
+      isBrowserType = _isBrowserType;
+    if (o == null || typeof o == "string" || typeof o == "number" || typeof o == "boolean" || dart.notNull(dart.dcall(isBrowserType, o))) {
       return o;
     } else if (o instanceof Date) {
       let ms = o.getTime();
       return new core.DateTime.fromMillisecondsSinceEpoch(dart.asInt(ms));
     } else if (dart.is(o, _DartObject) && dart.jsobject != dart.realRuntimeType(o)) {
       return dart.dload(o, _dartObj);
     } else {
       return _putIfAbsent(_dartProxies, o, _wrapToDart);
     }
   }
-  dart.fn(_convertToDart, core.Object, [dart.dynamic]);
+  dart.fn(_convertToDart, core.Object, [dart.dynamic], [dart.functionType(core.bool, [dart.dynamic])]);
   function _wrapToDart(o) {
     if (typeof o == "function") {
       return new JsFunction._fromJs(o);
     }
     if (o instanceof Array) {
       return new JsArray._fromJs(o);
     }
     return new JsObject._fromJs(o);
   }
   dart.fn(_wrapToDart, JsObject, [dart.dynamic]);
@@ skipping 39 matching lines @@
   });
   let __CastType0 = __CastType0$();
   // Exports:
   exports.JsObject = JsObject;
   exports.JsFunction = JsFunction;
   exports.JsArray$ = JsArray$;
   exports.JsArray = JsArray;
   exports.allowInterop = allowInterop;
   exports.allowInteropCaptureThis = allowInteropCaptureThis;
 });