Pass actual TestPlatform and OperatingSystem values to Suite.

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.
 
 library test.backend.metadata;
 
 import 'dart:collection';
 
 import '../backend/operating_system.dart';
 import '../backend/test_platform.dart';
@@ skipping 143 matching lines @@
     if (skipReason == null) skipReason = this.skipReason;
     if (onPlatform == null) onPlatform = this.onPlatform;
     return new Metadata(testOn: testOn, timeout: timeout, skip: skip,
         verboseTrace: verboseTrace, skipReason: skipReason,
         onPlatform: onPlatform);
   }
 
   /// Returns a copy of [this] with all platform-specific metadata from
   /// [onPlatform] resolved.
   Metadata forPlatform(TestPlatform platform, {OperatingSystem os}) {
+    if (onPlatform.isEmpty) return this;
+
     var metadata = this;
     onPlatform.forEach((platformSelector, platformMetadata) {
       if (!platformSelector.evaluate(platform, os: os)) return;
       metadata = metadata.merge(platformMetadata);
     });
     return metadata.change(onPlatform: {});
   }
 
   /// Serializes [this] into a JSON-safe object that can be deserialized using
   /// [new Metadata.deserialize].
@@ skipping 12 matching lines @@
             : timeout.duration.inMicroseconds,
         'scaleFactor': timeout.scaleFactor
       },
       'skip': skip,
       'skipReason': skipReason,
       'verboseTrace': verboseTrace,
       'onPlatform': serializedOnPlatform
     };
   }
 }