Add additional check to vmservice/websocket_client test.

tools/apps/update_homebrew/bin/update_homebrew.dart

Index: tools/apps/update_homebrew/bin/update_homebrew.dart
diff --git a/tools/apps/update_homebrew/bin/update_homebrew.dart b/tools/apps/update_homebrew/bin/update_homebrew.dart
index 91085c4818c5b2c9b6bdce3bd0ed9da6213f7eef..28b82cb486b07156351a18b95f9cfa4f4b849894 100644
--- a/tools/apps/update_homebrew/bin/update_homebrew.dart
+++ b/tools/apps/update_homebrew/bin/update_homebrew.dart
@@ -46,7 +46,7 @@ Future<String> getVersion(String channel, int revision) {
       .whenComplete(client.close);
 }
 
-Future<Map> setCurrentRevisions(Map revisions) {
+Future setCurrentRevisions(Map revisions) {
   return new File('$repository/dart.rb')
     .readAsLines()
     .then((lines) {
@@ -58,7 +58,7 @@ Future<Map> setCurrentRevisions(Map revisions) {
     });
 }
 
-Future<Map> setHashes(Map revisions, Map hashes) {
+Future setHashes(Map revisions, Map hashes) {
   List waitOn = [];
   for (var channel in CHANNELS) {
     hashes[channel] = {};