Don't exit() in test_progress but rather set io.exitCode

tools/testing/dart/test_progress.dart

 // Copyright (c) 2012, 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.
 
 library test_progress;
 
 import "dart:io";
+import "dart:io" as io;
 import "http_server.dart" as http_server;
 import "status_file_parser.dart";
 import "test_runner.dart";
 import "test_suite.dart";
 import "utils.dart";
 
 class ProgressIndicator {
   ProgressIndicator(this._startTime, this._printTiming)
       : _tests = [], _failureSummary = [];
 
@@ skipping 85 matching lines @@
     }
   }
 
   void allDone() {
     _printFailureSummary();
     _printStatus();
     _printSkippedCompilationInfo();
     _printTimingInformation();
     stdout.close();
     stderr.close();
-    if (_failedTests > 0) exit(1);
+    if (_failedTests > 0) {
+      io.exitCode = 1;
+    }
   }
 
   void _printStartProgress(TestCase test) {}
   void _printDoneProgress(TestCase test) {}
 
   String _pad(String s, int length) {
     StringBuffer buffer = new StringBuffer();
     for (int i = s.length; i < length; i++) {
       buffer.add(' ');
     }
@@ skipping 156 matching lines @@
     _printFailureSummary();
     _printSkippedCompilationInfo();
     _printTimingInformation();
     if (_failedTests > 0) {
       // We may have printed many failure logs, so reprint the summary data.
       _printProgress();
       print('');
     }
     stdout.close();
     stderr.close();
-    if (_failedTests > 0) exit(1);
+    if (_failedTests > 0) {
+      io.exitCode = 1;
+    }
   }
 
   void allTestsKnown() {
     if (!_allTestsKnown && SummaryReport.total > 0) {
       // Clear progress indicator before printing summary report.
       stdout.write(
           '\r                                               \r'.charCodes);
       SummaryReport.printReport();
     }
     _allTestsKnown = true;
@@ skipping 189 matching lines @@
       print('');
       print('$config:');
       statuses.sort((a, b) => a.compareTo(b));
       for (String status in statuses) {
         print('  $status');
       }
     });
     _printStatus();
   }
 }