fix some errors in our SDK, mostly around numbers

lib/runtime/dart/core.js

 dart_library.library('dart/core', null, /* Imports */[
   "dart_runtime/dart"
 ], /* Lazy imports */[
   'dart/_js_helper',
   'dart/_internal',
   'dart/collection',
   'dart/_interceptors',
   'dart/convert'
 ], function(exports, dart, _js_helper, _internal, collection, _interceptors, convert) {
   'use strict';
@@ skipping 589 matching lines @@
   Duration.MILLISECONDS_PER_HOUR = dart.notNull(Duration.MILLISECONDS_PER_MINUTE) * dart.notNull(Duration.MINUTES_PER_HOUR);
   Duration.MILLISECONDS_PER_DAY = dart.notNull(Duration.MILLISECONDS_PER_HOUR) * dart.notNull(Duration.HOURS_PER_DAY);
   Duration.SECONDS_PER_HOUR = dart.notNull(Duration.SECONDS_PER_MINUTE) * dart.notNull(Duration.MINUTES_PER_HOUR);
   Duration.SECONDS_PER_DAY = dart.notNull(Duration.SECONDS_PER_HOUR) * dart.notNull(Duration.HOURS_PER_DAY);
   Duration.MINUTES_PER_DAY = dart.notNull(Duration.MINUTES_PER_HOUR) * dart.notNull(Duration.HOURS_PER_DAY);
   Duration.ZERO = dart.const(new Duration({seconds: 0}));
   class Error extends Object {
     Error() {
     }
     static safeToString(object) {
-      if (dart.is(object, num) || typeof object == 'boolean' || null == object) {
+      if (typeof object == 'number' || typeof object == 'boolean' || null == object) {
         return dart.toString(object);
       }
       if (typeof object == 'string') {
         return Error._stringToSafeString(object);
       }
       return Error._objectToString(object);
     }
     static _stringToSafeString(string) {
       return _js_helper.jsonEncodeNative(string);
     }
@@ skipping 2745 matching lines @@
   exports.StackTrace = StackTrace;
   exports.Stopwatch = Stopwatch;
   exports.String = String;
   exports.RuneIterator = RuneIterator;
   exports.StringBuffer = StringBuffer;
   exports.StringSink = StringSink;
   exports.Symbol = Symbol;
   exports.Type = Type;
   exports.Uri = Uri;
 });