Respect top-level @TestOn declarations.

lib/src/runner/loader.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 unittest.runner.loader;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
 
+import 'package:analyzer/analyzer.dart';
 import 'package:path/path.dart' as p;
 
+import '../backend/metadata.dart';
 import '../backend/suite.dart';
 import '../backend/test_platform.dart';
 import '../util/dart.dart';
 import '../util/io.dart';
 import '../util/remote_exception.dart';
 import '../utils.dart';
 import 'browser/server.dart';
 import 'load_exception.dart';
+import 'parse_metadata.dart';
 import 'vm/isolate_test.dart';
 
 /// A class for finding test files and loading them into a runnable form.
 class Loader {
   /// All platforms for which tests should be loaded.
   final List<TestPlatform> _platforms;
 
   /// Whether to enable colors for Dart compilation.
   final bool _color;
 
@@ skipping 44 matching lines @@
       // TODO(nweiz): Provide a way for the caller to gracefully handle some
       // suites failing to load without stopping the rest.
       return loadFile(entry.path);
     })).then((suites) => flatten(suites));
   }
 
   /// Loads a test suite from the file at [path].
   ///
   /// This will throw a [LoadException] if the file fails to load.
   Future<List<Suite>> loadFile(String path) {
+    var metadata;
+    try {
+      metadata = parseMetadata(path);
+    } on AnalyzerErrorGroup catch (_) {
+      // Ignore the analyzer's error, since its formatting is much worse than
+      // the VM's or dart2js's.
+      metadata = new Metadata();
+    } on FormatException catch (error) {
+      throw new LoadException(path, error);
+    }
+
     return Future.wait(_platforms.map((platform) {
-      if (platform == TestPlatform.chrome) return _loadBrowserFile(path);
-      assert(platform == TestPlatform.vm);
-      return _loadVmFile(path);
-    }));
+      return new Future.sync(() {
+        if (!metadata.testOn.evaluate(platform, os: currentOS)) return null;
+
+        if (platform == TestPlatform.chrome) return _loadBrowserFile(path);
+        assert(platform == TestPlatform.vm);
+        return _loadVmFile(path);
+      }).then((suite) =>
+          suite == null ? null : suite.change(metadata: metadata));
+    })).then((suites) => suites.where((suite) => suite != null).toList());
   }
 
   /// Load the test suite at [path] in a browser.
   Future<Suite> _loadBrowserFile(String path) =>
       _browserServer.then((browserServer) => browserServer.loadSuite(path));
 
   /// Load the test suite at [path] in VM isolate.
   Future<Suite> _loadVmFile(String path) {
     var packageRoot = packageRootFor(path, _packageRoot);
     var receivePort = new ReceivePort();
@@ skipping 35 matching lines @@
   Future close() {
     for (var isolate in _isolates) {
       isolate.kill();
     }
     _isolates.clear();
 
     if (_browserServerCompleter == null) return new Future.value();
     return _browserServer.then((browserServer) => browserServer.close());
   }
 }