Print error output from DumpRenderTree updater in test.dart.

tools/testing/dart/drt_updater.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("drt_updater");
 
 #import("dart:io");
 
 class _DartiumUpdater {
   String name;
   String script;
   String option;
 
   bool isActive = false;
   bool updated = false;
   List onUpdated;
 
-  Process _updatingProcess;
+  Future<ProcessResult> _updatingProcess;
 
   _DartiumUpdater(this.name, this.script, [this.option = null]);
 
   void update() {
     if (!isActive) {
       isActive = true;
       print('Updating $name.');
       onUpdated = [() {updated = true;} ];
-      _updatingProcess = Process.start('python', _getUpdateCommand);
-      _updatingProcess.onExit = _onUpdatedHandler;
-      _updatingProcess.onError = (error) {
-        print("Error starting $script process: $error");
-        _onUpdatedHandler(-1);  // Continue anyway.
-      };
+      _updatingProcess = Process.run('python', _getUpdateCommand);
+      _updatingProcess.handleException((e) {
+        print("Error starting $script process: $e");
+        return false;
+      });
+      _updatingProcess.then(_onUpdatedHandler);
     }
   }
 
   List<String> get _getUpdateCommand {
-    String scriptPath = new Options().script.replaceAll('\\', '/');
-    String toolsDir = scriptPath.substring(0, scriptPath.lastIndexOf('/'));
-    List<String> command = ['$toolsDir/$script'];
+    Path testScriptPath = new Path.fromNative(new Options().script);
+    Path updateScriptPath = testScriptPath.directoryPath.append(script);
+    List<String> command = [updateScriptPath.toNativePath()];
     if (null !== option) {
       command.add(option);
     }
     return command;
   }
 
-  void _onUpdatedHandler(int exit_code) {
-    print('$name updated ($exit_code)');
+  void _onUpdatedHandler(ProcessResult result) {
+    if (result.exitCode == 0) {
+      print('$name updated');
+    } else {
+      print('Failure updating $name');
+      print('  Exit code: ${result.exitCode}');
+      print(result.stdout);
+      print(result.stderr);
+      exit(1);
+    }
     for (var callback in onUpdated ) callback();
   }
 }
 
 _DartiumUpdater _dumpRenderTreeUpdater;
 _DartiumUpdater _dartiumUpdater;
 
 _DartiumUpdater runtimeUpdater(Map configuration) {
   String runtime = configuration['runtime'];
   if (runtime == 'drt' && configuration['drt'] == '') {
     // Download the default DumpRenderTree from Google Storage.
     if (_dumpRenderTreeUpdater === null) {
       _dumpRenderTreeUpdater = new _DartiumUpdater('DumpRenderTree',
                                                    'get_archive.py', 'drt');
     }
     return _dumpRenderTreeUpdater;
   } else if (runtime == 'dartium' && configuration['dartium'] == '') {
     // Download the default Dartium from Google Storage.
     if (_dartiumUpdater === null) {
       _dartiumUpdater = new _DartiumUpdater('Dartium Chrome', 'get_archive.py',
                                             'dartium');
     }
     return _dartiumUpdater;
   } else {
     return null;
   }
 }