Remove deprecated StringBuffer.add, addAll and addCharCode.

utils/tests/peg/peg_test.dart

Index: utils/tests/peg/peg_test.dart
diff --git a/utils/tests/peg/peg_test.dart b/utils/tests/peg/peg_test.dart
index 59d2d5570b9c9ed825027cf5ff4d7f97ef8b6b94..692dc1518e7b6c2b9c08772d85908feab0fb1334 100644
--- a/utils/tests/peg/peg_test.dart
+++ b/utils/tests/peg/peg_test.dart
@@ -322,14 +322,14 @@ void check(grammar, rule, input, expected) {
 printList(item) {
   if (item is List) {
     StringBuffer sb = new StringBuffer();
-    sb.add('[');
+    sb.write('[');
     var sep = '';
     for (var x in item) {
-      sb.add(sep);
-      sb.add(printList(x));
+      sb.write(sep);
+      sb.write(printList(x));
       sep = ',';
     }
-    sb.add(']');
+    sb.write(']');
     return sb.toString();
   }
   if (item == null)