Move js library back into compiler directory.

sdk/lib/_internal/compiler/js_lib/preambles/jsshell.js

 // Copyright (c) 2014, 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.
 
 // Javascript preamble, that lets the output of dart2js run on JSShell.
 
 (function(self) {
   // Using strict mode to avoid accidentally defining global variables.
   "use strict"; // Should be first statement of this function.
 
   // Location (Uri.base)
 
   var workingDirectory = environment["PWD"];
   self.location = { href: "file://" + workingDirectory + "/" };
 
   // Global properties. "self" refers to the global object, so adding a
   // property to "self" defines a global variable.
   self.self = self;
 })(this)