Change dart:io to use Future for one-shot operations.

tools/testing/dart/drt_updater.dart

Index: tools/testing/dart/drt_updater.dart
diff --git a/tools/testing/dart/drt_updater.dart b/tools/testing/dart/drt_updater.dart
index 4a42482e71b61fe7c6f738ea9ff4dba54eda6655..a45599783dd27d8b08e26d237684a6712da7f036 100644
--- a/tools/testing/dart/drt_updater.dart
+++ b/tools/testing/dart/drt_updater.dart
@@ -16,7 +16,7 @@ class _DartiumUpdater {
   bool updated = false;
   List onUpdated;
 
-  Process _updatingProcess;
+  InteractiveProcess _updatingProcess;
 
   _DartiumUpdater(this.name, this.script, [this.option = null]);
 
@@ -25,7 +25,7 @@ class _DartiumUpdater {
       isActive = true;
       print('Updating $name.');
       onUpdated = [() {updated = true;} ];
-      _updatingProcess = new Process.start('python', _getUpdateCommand);
+      _updatingProcess = Process.start('python', _getUpdateCommand);
       _updatingProcess.onExit = _onUpdatedHandler;
       _updatingProcess.onError = (error) {
         print("Error starting $script process: $error");