reenable --checked option in flutter drive (#3916)

packages/flutter_tools/lib/src/commands/drive.dart

@@ -269,7 +269,8 @@ Future<int> startApp(DriveCommand command, BuildMode buildMode) async {
     mainPath: mainPath,
     route: command.route,
     debuggingOptions: new DebuggingOptions.enabled(
-      checked: buildMode == BuildMode.debug,
+      // TODO(devoncarew): Change this to 'buildMode == BuildMode.debug'.
+      checked: command.argResults['checked'],
       startPaused: true,
       observatoryPort: command.debugPort
     ),