Move pub into sdk/lib/_internal.

sdk/lib/_internal/pub/lib/src/validator/compiled_dartdoc.dart

 // Copyright (c) 2012, 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.
 
 library compiled_dartdoc_validator;
 
 import 'dart:async';
 
 import 'package:pathos/path.dart' as path;
 
@@ skipping 26 matching lines @@
         if (files.every((val) => fileExists(val))) {
           warnings.add("Avoid putting generated documentation in "
                   "${path.relative(dir)}.\n"
               "Generated documentation bloats the package with redundant "
                   "data.");
         }
       }
     });
   }
 }