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..a459bc9cc41bbad352b471b7f7eaebd714f56068 100644
--- a/pkg/analyzer_cli/test/perf_report_test.dart
+++ b/pkg/analyzer_cli/test/perf_report_test.dart
@@ -9,11 +9,13 @@ import 'dart:convert' show JSON;
 import 'package:analyzer_cli/src/options.dart';
 import 'package:analyzer_cli/src/perf_report.dart';
 import 'package:unittest/unittest.dart';
+import 'package:analyzer/src/generated/engine.dart';
 
 main() {
   test('makePerfReport', () {
     var options = CommandLineOptions.parse(["somefile.dart"]);
-    var encoded = makePerfReport(1000, 1234, options);
+    var context = AnalysisEngine.instance.createAnalysisContext();
+    var encoded = makePerfReport(1000, 1234, options, context);
 
     var json = JSON.decode(encoded);
     expect(json['totalElapsedTime'], 234);