Get rid of library proto information for debugger libraries

lib/runtime/dart_library.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 file defines the module loader for the dart runtime.
 */
 
 var dart_library =
   typeof module != "undefined" && module.exports || {};
 
@@ skipping 66 matching lines @@
   LibraryLoader.READY = 2;
 
   // Map from name to LibraryLoader
   let libraries = new Map();
   dart_library.libraries = function() { return libraries.keys(); };
   dart_library.debuggerLibraries = function() {
     var debuggerLibraries = [];
     libraries.forEach(function (value, key, map) {
       debuggerLibraries.push(value.load());
     });
+    debuggerLibraries.__proto__ = null;
     return debuggerLibraries;
   };
 
   function library(name, defaultValue, imports, loader) {
     let result = new LibraryLoader(name, defaultValue, imports, loader);
     libraries.set(name, result);
     return result;
   }
   dart_library.library = library;
 
@@ skipping 57 matching lines @@
         window.SourceBufferList = new MediaSource().sourceBuffers.constructor;
       }
     }
 
     // This import is only needed for chrome debugging. We should provide an
     // option to compile without it.
     dart_sdk._debugger.registerDevtoolsFormatter();
   }
 
 })(dart_library);