Move js library back into compiler directory.

sdk/lib/_internal/compiler/js_lib/preambles/d8.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 V8's d8 shell.
 
 // Node wraps files and provides them with a different `this`. The global
 // `this` can be accessed through `global`.
 
 var self = this;
@@ skipping 263 matching lines @@
     var action = function() { main(args); }
     eventLoop(action);
   };
   self.setTimeout = addTimer;
   self.clearTimeout = cancelTimer;
   self.setInterval = addInterval;
   self.clearInterval = cancelTimer;
   self.scheduleImmediate = addTask;
   self.self = self;
 })(self);