Simplify CommandOutput and friends.

tools/testing/dart/browser_controller.dart

Index: tools/testing/dart/browser_controller.dart
diff --git a/tools/testing/dart/browser_controller.dart b/tools/testing/dart/browser_controller.dart
index ce5ad9053234ffe786aaa004c38e2778424c2ed7..3700a29aeb6814ea3252307f52b91ce5a7ff01f4 100644
--- a/tools/testing/dart/browser_controller.dart
+++ b/tools/testing/dart/browser_controller.dart
@@ -505,10 +505,9 @@ class Chrome extends Browser {
           "--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());