Hide some names from package:collection.

lib/src/backend/metadata.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.
 
 import 'dart:collection';
 
 import 'package:boolean_selector/boolean_selector.dart';
-import 'package:collection/collection.dart';
+import 'package:collection/collection.dart' hide mapMap, mergeMaps;
 
 import '../frontend/skip.dart';
 import '../frontend/timeout.dart';
 import '../utils.dart';
 import 'operating_system.dart';
 import 'platform_selector.dart';
 import 'test_platform.dart';
 
 /// Metadata for a test or test suite.
 ///
@@ skipping 297 matching lines @@
   _serializeTimeout(Timeout timeout) {
     if (timeout == Timeout.none) return 'none';
     return {
       'duration': timeout.duration == null
           ? null
           : timeout.duration.inMicroseconds,
       'scaleFactor': timeout.scaleFactor
     };
   }
 }