TBR: Removed const from CustomMatcher constructor. dartc doesn't like it.

pkg/unittest/test/matchers_test.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 unittestTests;
 import 'package:unittest/unittest.dart';
 import 'dart:async';
 import 'dart:collection';
 part 'test_utils.dart';
 
@@ skipping 12 matching lines @@
     description.add('a string starting with ').
         addDescriptionOf(collapseWhitespace(_prefix)).
         add(' ignoring whitespace');
 }
 
 class Widget {
   int price;
 }
 
 class HasPrice extends CustomMatcher {
-  const HasPrice(matcher) :
+  HasPrice(matcher) :
     super("Widget with a price that is", "price", matcher);
   featureValueOf(actual) => actual.price;
 }
 
 class SimpleIterable extends IterableBase {
   int count;
   SimpleIterable(this.count);
 
   bool contains(int val) => count < val ? false : true;
 
@@ skipping 665 matching lines @@
       w.price = 10;
       shouldPass(w, new HasPrice(10));
       shouldPass(w, new HasPrice(greaterThan(0)));
       shouldFail(w, new HasPrice(greaterThan(10)),
           'Expected: Widget with a price that is a value greater than <10> '
           'but: price was <10>.');
     });
   });
 }