Don't print "Necessary status file updates:" if there are none.

tools/testing/dart/test_progress.dart

 // Copyright (c) 2013, 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:convert' show JSON;
 import 'dart:io';
 
 import "package:status_file/expectation.dart";
 
 import 'command.dart';
@@ skipping 320 matching lines @@
   }
 
   String _extractRuntime(String configuration) {
     // Extract runtime from a configuration, for example,
     // 'none-vm-checked release_ia32'.
     List<String> runtime = configuration.split(' ')[0].split('-');
     return '${runtime[0]}-${runtime[1]}';
   }
 
   void _printFailureSummary() {
-    var groupedStatuses = new Map<String, List<String>>();
-    statusToConfigs.forEach((String status, List<String> configs) {
-      var runtimeToConfiguration = new Map<String, List<String>>();
-      for (String config in configs) {
-        String runtime = _extractRuntime(config);
-        var runtimeConfigs =
-            runtimeToConfiguration.putIfAbsent(runtime, () => <String>[]);
-        runtimeConfigs.add(config);
+    var groupedStatuses = <String, List<String>>{};
+    statusToConfigs.forEach((status, configs) {
+      var runtimeToConfiguration = <String, List<String>>{};
+      for (var config in configs) {
+        var runtime = _extractRuntime(config);
+        runtimeToConfiguration
+            .putIfAbsent(runtime, () => <String>[])
+            .add(config);
       }
-      runtimeToConfiguration
-          .forEach((String runtime, List<String> runtimeConfigs) {
+
+      runtimeToConfiguration.forEach((runtime, runtimeConfigs) {
         runtimeConfigs.sort((a, b) => a.compareTo(b));
-        List<String> statuses = groupedStatuses.putIfAbsent(
+        var statuses = groupedStatuses.putIfAbsent(
             '$runtime: $runtimeConfigs', () => <String>[]);
         statuses.add(status);
       });
     });
 
+    if (groupedStatuses.isEmpty) return;
+
     print('\n\nNecessary status file updates:');
     groupedStatuses.forEach((String config, List<String> statuses) {
       print('');
       print('$config:');
       statuses.sort((a, b) => a.compareTo(b));
-      for (String status in statuses) {
+      for (var status in statuses) {
         print('  $status');
       }
     });
   }
 }
 
 class SkippedCompilationsPrinter extends EventListener {
   int _skippedCompilations = 0;
 
   void done(TestCase test) {
@@ skipping 294 matching lines @@
 }
 
 String _buildSummaryEnd(int failedTests) {
   if (failedTests == 0) {
     return '\n===\n=== All tests succeeded\n===\n';
   } else {
     var pluralSuffix = failedTests != 1 ? 's' : '';
     return '\n===\n=== ${failedTests} test$pluralSuffix failed\n===\n';
   }
 }