add --x-package-warnings-prefix option to dartanalyzer

pkg/analyzer_cli/test/perf_report_test.dart

Index: pkg/analyzer_cli/test/perf_report_test.dart
diff --git a/pkg/analyzer_cli/test/perf_report_test.dart b/pkg/analyzer_cli/test/perf_report_test.dart
index f668485b044e1059c57356ebec25814605b297cf..19d91a121de60657b270c692e4e4b08d20c0f139 100644
--- a/pkg/analyzer_cli/test/perf_report_test.dart
+++ b/pkg/analyzer_cli/test/perf_report_test.dart
@@ -6,6 +6,7 @@ library analyzer_cli.test.perf_report;
 
 import 'dart:convert' show JSON;
 
+import 'package:analyzer_cli/src/error_formatter.dart' show AnalysisStats;
 import 'package:analyzer_cli/src/options.dart';
 import 'package:analyzer_cli/src/perf_report.dart';
 import 'package:unittest/unittest.dart';
@@ -13,7 +14,7 @@ import 'package:unittest/unittest.dart';
 main() {
   test('makePerfReport', () {
     var options = CommandLineOptions.parse(["somefile.dart"]);
-    var encoded = makePerfReport(1000, 1234, options);
+    var encoded = makePerfReport(1000, 1234, options, 0, new AnalysisStats());
 
     var json = JSON.decode(encoded);
     expect(json['totalElapsedTime'], 234);