fix some errors in our SDK, mostly around numbers

lib/runtime/_operations.js

 // 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.
 
 /* This library defines runtime operations on objects used by the code
  * generator.
  */
 dart_library.library('dart_runtime/_operations', null, /* Imports */[
 ], /* Lazy Imports */[
   'dart/async',
@@ skipping 214 matching lines @@
     let actual = rtti.realRuntimeType(obj);
     if (types.isGroundType(type)) errors.throwCastError(actual, type);
 
     if (_ignoreTypeFailure(actual, type)) return obj;
 
     dart_utils.throwStrongModeError('Strong mode cast failure from ' +
       types.typeName(actual) + ' to ' + types.typeName(type));
   }
   exports.cast = cast;
 
+  function asInt(obj) {
+    if (Math.floor(obj) != obj) {
+      // Note: null will also be caught by this check
+      errors.throwCastError(rtti.realRuntimeType(obj), core.int);
+    }
+    return obj;
+  }
+  exports.asInt = asInt;
+
   function arity(f) {
     // TODO(jmesserly): need to parse optional params.
     // In ES6, length is the number of required arguments.
     return { min: f.length, max: f.length };
   }
   exports.arity = arity;
 
   function equals(x, y) {
     if (x == null || y == null) return x == y;
     let eq = x['=='];
@@ skipping 203 matching lines @@
     next() {
       let i = this.dartIterator;
       let done = !i.moveNext();
       return { done: done, value: done ? void 0 : i.current };
     }
   }
   exports.JsIterator = JsIterator;
 
 
 });