Refactor runtime into libraries, better type reps

lib/runtime/_errors.js

Index: lib/runtime/_errors.js
diff --git a/lib/runtime/_errors.js b/lib/runtime/_errors.js
new file mode 100644
index 0000000000000000000000000000000000000000..32b6ae01a8e1c245d94fa64b0d5f227e4b57f21f
--- /dev/null
+++ b/lib/runtime/_errors.js
@@ -0,0 +1,31 @@
+// 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 encapsulates the core sdk errors that the runtime knows about.
+ *
+ */
+
+dart_library.library('dart_runtime/_errors', null, /* Imports */[
+], /* Lazy Imports */[
+  'dart/core',
+  'dart/_js_helper'
+], function(exports, core, _js_helper) {
+  'use strict';
+
+  function throwNoSuchMethod(obj, name, pArgs, nArgs, extras) {
+    throw new core.NoSuchMethodError(obj, name, pArgs, nArgs, extras);
+  }
+  exports.throwNoSuchMethod = throwNoSuchMethod;
+
+  function throwCastError(actual, type) {
+    throw new _js_helper.CastErrorImplementation(actual, type);
+  }
+  exports.throwCastError = throwCastError;
+
+  function throwAssertionError() {
+    throw new core.AssertionError();
+  }
+  exports.throwAssertionError = throwAssertionError;
+});