Clean up package imports and library names

pkg/analyzer/lib/src/util/asserts.dart

 // 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.
 
-library engine.utilities.asserts;
+library analyzer.src.util.asserts;
 
 /**
  * Ensures that the given [value] is not null.
  * Otherwise throws an [ArgumentError].
  * An optional [description] is used in the error message.
  */
 void notNull(Object value, [String description]) {
   if (value == null) {
     if (description == null) {
       throw new ArgumentError('Must not be null');
     } else {
       throw new ArgumentError('Must not be null: $description');
     }
   }
 }