Remove deprecated StringBuffer.add, addAll and addCharCode.

tests/compiler/dart2js/unparser_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:uri';
 import 'parser_helper.dart';
 import 'mock_compiler.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/tree/tree.dart';
 
 testUnparse(String statement) {
@@ skipping 288 matching lines @@
   testUnparseTopLevelWithMetadata('typedef C = S<A,B> with M;');
 
   testUnparseTopLevelWithMetadata('typedef C = S with M<A>;');
   testUnparseTopLevelWithMetadata('typedef C = S with M<A,B>;');
   testUnparseTopLevelWithMetadata('typedef C = S with M1<A>,M2;');
   testUnparseTopLevelWithMetadata('typedef C = S with M1,M2<A,B>;');
 }
 
 testUnparseParameters(List<String> variableDeclarations) {
   var sb = new StringBuffer();
-  sb.add('Constructor(');
+  sb.write('Constructor(');
   int index = 0;
   for (String variableDeclaration in variableDeclarations) {
     if (index != 0) {
-      sb.add(', ');
+      sb.write(', ');
     }
-    sb.add(variableDeclaration);
+    sb.write(variableDeclaration);
     index++;
   }
-  sb.add(');');
+  sb.write(');');
 
   FunctionExpression node = parseMember(sb.toString());
   index = 0;
   for (VariableDefinitions parameter in node.parameters.nodes) {
     Expect.equals(variableDeclarations[index], unparse(parameter));
     index++;
   }
 
 }
 
@@ skipping 27 matching lines @@
   testImport();
   testExport();
   testPart();
   testPartOf();
   testCombinators();
   testRedirectingFactoryConstructors();
   testClassDeclarations();
   testMixinApplications();
   testParameters();
 }