Simplify CommandOutput and friends.

tools/testing/dart/browser_controller.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:async';
 import 'dart:convert';
 import 'dart:core';
 import 'dart:io';
 import 'dart:math';
 
@@ skipping 487 matching lines @@
         };
         var args = [
           "--user-data-dir=${userDir.path}",
           url,
           "--disable-extensions",
           "--disable-popup-blocking",
           "--bwsi",
           "--no-first-run",
         ];
 
-        // TODO(rnystrom): If you want Chrome to spawn with the dev tools tab
-        // open, which is handy for debugging, add:
-        //
-        //     --auto-open-devtools-for-tabs
+        // TODO(rnystrom): Uncomment this to open the dev tools tab when Chrome
+        // is spawned. Handy for debugging tests.
+        // args.add("--auto-open-devtools-for-tabs");
 
         return startBrowserProcess(_binary, args,
             environment: _getEnvironment());
       });
     }).catchError((e) {
       _logEvent("Running $_binary --version failed with $e");
       return false;
     });
   }
 
@@ skipping 1424 matching lines @@
           'exit code: ${result.exitCode}\n'
           'stdout: ${result.stdout}\n'
           'stderr: ${result.stderr}');
     } else {
       print('[$message] Successfully uploaded screenshot to $storageUrl');
     }
     new File(screenshotFile).deleteSync();
   }
   print('--------------------------------------------------------------------');
 }