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

tests/standalone/io/regress_7191_test.dart

Index: tests/standalone/io/regress_7191_test.dart
diff --git a/tests/standalone/io/regress_7191_test.dart b/tests/standalone/io/regress_7191_test.dart
index 0262f4d1942448e4d95166283ec050c1c5774642..8c56fb356e7b0bd78ff4f42269c9fef89d9b7e1e 100644
--- a/tests/standalone/io/regress_7191_test.dart
+++ b/tests/standalone/io/regress_7191_test.dart
@@ -19,9 +19,9 @@ main() {
   var scriptDir = new Path(options.script).directoryPath;
   var script = scriptDir.append('regress_7191_script.dart').toNativePath();
   Process.start(executable, [script]).then((process) {
-    process.stdin.writeBytes([0]);
+    process.stdin.add([0]);
     process.stdout.listen((_) { },
-                           onDone: () { process.stdin.writeBytes([0]); });
+                           onDone: () { process.stdin.add([0]); });
     process.stderr.listen((_) { });
     process.exitCode.then((exitCode) {
       port.close();