Move runtime js files down to lib/runtime/dart

lib/runtime/dart/_errors.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 encapsulates the core sdk errors that the runtime knows about.
  *
  */
 
-dart_library.library('dart_runtime/_errors', null, /* Imports */[
+dart_library.library('dart/_errors', null, /* Imports */[
 ], /* Lazy Imports */[
-  'dart_runtime/_operations',
+  'dart/_operations',
   'dart/core',
   'dart/_js_helper'
 ], function(exports, operations, core, _js_helper) {
   'use strict';
 
   function throwNoSuchMethod(obj, name, pArgs, nArgs, extras) {
     operations.throw(new core.NoSuchMethodError(obj, name, pArgs, nArgs, extras));
   }
   exports.throwNoSuchMethod = throwNoSuchMethod;
 
   function throwCastError(actual, type) {
     operations.throw(new _js_helper.CastErrorImplementation(actual, type));
   }
   exports.throwCastError = throwCastError;
 
   function throwAssertionError() {
     operations.throw(new core.AssertionError());
   }
   exports.throwAssertionError = throwAssertionError;
 
   function throwNullValueError() {
     // TODO(vsm): Per spec, we should throw an NSM here.  Technically, we ought
     // to thread through method info, but that uglifies the code and can't
     // actually be queried ... it only affects how the error is printed.
     operations.throw(new core.NoSuchMethodError(null,
       new core.Symbol('<Unexpected Null Value>'), null, null, null));
   }
   exports.throwNullValueError = throwNullValueError;
 });