Remove StreamSink(replaced by EventSink) and make IOSink extend EventSink.

tests/standalone/io/http_head_test.dart

Index: tests/standalone/io/http_head_test.dart
diff --git a/tests/standalone/io/http_head_test.dart b/tests/standalone/io/http_head_test.dart
index cac1dd902c53bb3c5f70f18fb519d3541ebe9ad8..ea5974b6ca1a1ee5d1f97c9085dd2034260c83ea 100644
--- a/tests/standalone/io/http_head_test.dart
+++ b/tests/standalone/io/http_head_test.dart
@@ -15,15 +15,15 @@ void testHEAD(int totalConnections) {
         } else if (request.uri.path == "/test200") {
           response.contentLength = 200;
           List<int> data = new List<int>.filled(200, 0);
-          response.writeBytes(data);
+          response.add(data);
           response.close();
         } else if (request.uri.path == "/testChunked100") {
           List<int> data = new List<int>.filled(100, 0);
-          response.writeBytes(data);
+          response.add(data);
           response.close();
         } else if (request.uri.path == "/testChunked200") {
           List<int> data = new List<int>.filled(200, 0);
-          response.writeBytes(data);
+          response.add(data);
           response.close();
         } else {
           assert(false);