Remove deprecated StringBuffer.add, addAll and addCharCode.

tests/language/call_operator_test.dart

Index: tests/language/call_operator_test.dart
diff --git a/tests/language/call_operator_test.dart b/tests/language/call_operator_test.dart
index 2dc70701b6de98fd88f89188105814fb9a3488c0..c3e285834dbe00d4eba58ef5fbff9e93fe404d9b 100644
--- a/tests/language/call_operator_test.dart
+++ b/tests/language/call_operator_test.dart
@@ -32,9 +32,9 @@ class E {
   String call(String str, {int count: 1}) {
     StringBuffer buffer = new StringBuffer();
     for (var i = 0; i < count; i++) {
-      buffer.add(str);
+      buffer.write(str);
       if (i < count - 1) {
-        buffer.add(":");
+        buffer.write(":");
       }
     }
     return buffer.toString();