Make IOSink implement StringSink

tests/standalone/io/http_server_response_test.dart

Index: tests/standalone/io/http_server_response_test.dart
diff --git a/tests/standalone/io/http_server_response_test.dart b/tests/standalone/io/http_server_response_test.dart
index fc948762be0a7f97b2dbbfcd37b76e5c4d7d605d..c95b2ed637a4b7e20013aeb8d26fb18b6ff834cc 100644
--- a/tests/standalone/io/http_server_response_test.dart
+++ b/tests/standalone/io/http_server_response_test.dart
@@ -87,7 +87,7 @@ void testResponseAddStream() {
 void testBadResponseAdd() {
   testServerRequest((server, request) {
     request.response.contentLength = 0;
-    request.response.add([0]);
+    request.response.writeBytes([0]);
     request.response.done.catchError((error) {
       server.close();
     }, test: (e) => e is HttpException);
@@ -95,8 +95,8 @@ void testBadResponseAdd() {
 
   testServerRequest((server, request) {
     request.response.contentLength = 5;
-    request.response.add([0, 0, 0]);
-    request.response.add([0, 0, 0]);
+    request.response.writeBytes([0, 0, 0]);
+    request.response.writeBytes([0, 0, 0]);
     request.response.done.catchError((error) {
       server.close();
     }, test: (e) => e is HttpException);
@@ -104,9 +104,9 @@ void testBadResponseAdd() {
 
   testServerRequest((server, request) {
     request.response.contentLength = 0;
-    request.response.add(new Uint8List(64 * 1024));
-    request.response.add(new Uint8List(64 * 1024));
-    request.response.add(new Uint8List(64 * 1024));
+    request.response.writeBytes(new Uint8List(64 * 1024));
+    request.response.writeBytes(new Uint8List(64 * 1024));
+    request.response.writeBytes(new Uint8List(64 * 1024));
     request.response.done.catchError((error) {
       server.close();
     }, test: (e) => e is HttpException);
@@ -124,7 +124,7 @@ void testBadResponseClose() {
 
   testServerRequest((server, request) {
     request.response.contentLength = 5;
-    request.response.add([0]);
+    request.response.writeBytes([0]);
     request.response.close();
     request.response.done.catchError((error) {
       server.close();