Fix problems that occur in checked mode.

lib/unittest/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.
 
 /**
  * Returns a matcher which matches [Collection]s in which all elements
  * match the given [matcher].
  */
 Matcher everyElement(matcher) => new _EveryElement(wrapMatcher(matcher));
 
@@ skipping 89 matching lines @@
       for (var element in item) {
         ++actualLength;
       }
     }
     if (expectedLength > actualLength) {
       return 'has too few elements (${actualLength} < ${expectedLength})';
     } else if (expectedLength < actualLength) {
       return 'has too many elements (${actualLength} > ${expectedLength})';
     }
     List<bool> matched = new List<bool>(actualLength);
+    for (var i = 0; i < actualLength; i++) {
+      matched[i] = false;
+    }
     var expectedPosition = 0;
     for (var expectedElement in _expected) {
       var actualPosition = 0;
       var gotMatch = false;
       for (var actualElement in item) {
         if (!matched[actualPosition]) {
           if (expectedElement == actualElement) {
             matched[actualPosition] = gotMatch = true;
             break;
           }
@@ skipping 28 matching lines @@
   Description describeMismatch(item, Description mismatchDescription) {
     if (item is !Collection) {
       return mismatchDescription.
           addDescriptionOf(item).
           add(' not a collection');
     } else {
       return super.describeMismatch(item, mismatchDescription);
     }
   }
 }