fasta.BeginGroupToken implement analyzer.BeginToken

pkg/front_end/test/precedence_info_test.dart

Index: pkg/front_end/test/precedence_info_test.dart
diff --git a/pkg/front_end/test/precedence_info_test.dart b/pkg/front_end/test/precedence_info_test.dart
index 6783a6650607d88dced8c6f74159226983fa9925..473dd1b33f0970b7762d2fce4b76626203031304 100644
--- a/pkg/front_end/test/precedence_info_test.dart
+++ b/pkg/front_end/test/precedence_info_test.dart
@@ -457,7 +457,7 @@ class PrecedenceInfoTest {
       for (String source in lexemes) {
         var scanner = new StringScanner(source, includeComments: true);
         var token = scanner.tokenize();
-        expect(token.type.precedence, precedence, reason: source);
+        expect(token.info.precedence, precedence, reason: source);
       }
     });
   }