Add tests for BuildGroup names

tools/gardening/lib/src/client.dart

 // Copyright (c) 2017, 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:async';
-import 'dart:io';
+import 'dart:io' hide HttpException;
 
 import 'buildbot_data.dart';
 import 'buildbot_loading.dart';
 import 'buildbot_structures.dart';
 import 'logdog.dart';
 import 'util.dart';
 
 /// Interface for pulling build bot results.
 abstract class BuildbotClient {
   /// Reads the [BuildResult] for the [buildUri].
   Future<BuildResult> readResult(BuildUri buildUri);
 
   int get mostRecentBuildNumber;
 
   /// Closes the client and cleans up its state.
   void close();
 }
 
 /// Buildbot client that pulls build bot results through http.
 class HttpBuildbotClient implements BuildbotClient {
   final HttpClient _client = new HttpClient();
 
   @override
-  Future<BuildResult> readResult(BuildUri buildUri) {
-    return readBuildResultFromHttp(_client, buildUri);
+  Future<BuildResult> readResult(BuildUri buildUri) async {
+    try {
+      return await readBuildResultFromHttp(_client, buildUri);
+    } on HttpException {
+      return null;
+    }
   }
 
   int get mostRecentBuildNumber => -2;
 
   @override
   void close() {
     _client.close();
   }
 }
 
@@ skipping 41 matching lines @@
         buildUri = buildUri.withBuildNumber(buildNumber);
       }
     }
   }
 
   @override
   void close() {
     // Nothing to do.
   }
 }