Fix issue 8218: "part of" directive comes after dartdoc comment.

pkg/unittest/lib/src/collection_matchers.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.
 
+part of matcher;
+
 /**
  * Returns a matcher which matches [Collection]s in which all elements
  * match the given [matcher].
  */
-
-part of matcher;
-
 Matcher everyElement(matcher) => new _EveryElement(wrapMatcher(matcher));
 
 class _EveryElement extends _CollectionMatcher {
   Matcher _matcher;
 
   _EveryElement(Matcher this._matcher);
 
   bool matches(item, MatchState matchState) {
     if (item is! Iterable) {
       return false;
@@ skipping 171 matching lines @@
     if (item is !Collection) {
       return mismatchDescription.
           addDescriptionOf(item).
           add(' not a collection');
     } else {
       return super.describeMismatch(item, mismatchDescription, matchState,
         verbose);
     }
   }
 }