Make parser and scanner suites able to run standalone.

pkg/front_end/test/fasta/scanner/scanner_suite.dart

Index: pkg/front_end/test/fasta/scanner/scanner_suite.dart
diff --git a/pkg/front_end/test/fasta/scanner/scanner_suite.dart b/pkg/front_end/test/fasta/scanner/scanner_suite.dart
index ba48f082b08ba01eee1fddf87dc9ac0e1635f0ac..62db21dda72943a9af0e203885e6d30d96e8bfa5 100644
--- a/pkg/front_end/test/fasta/scanner/scanner_suite.dart
+++ b/pkg/front_end/test/fasta/scanner/scanner_suite.dart
@@ -13,9 +13,10 @@ Future<ChainContext> createContext(
 
 class ScannerContext extends ChainContext {
   final List<Step> steps = const <Step>[
-      const Read(),
-      const Scan(),
+    const Read(),
+    const Scan(),
   ];
 }
 
-main(List<String> arguments) => runMe(arguments, createContext);
+main(List<String> arguments) =>
+    runMe(arguments, createContext, "../testing.json");