Don't delay IOSink.close() with no subscription to the next instance.

utils/pub/io.dart

Index: utils/pub/io.dart
diff --git a/utils/pub/io.dart b/utils/pub/io.dart
index 13516223b2d9551cd47c13ab2b20de63378fb6c5..50889289ab1edc7dba6a6a548f353b4d76cf0664 100644
--- a/utils/pub/io.dart
+++ b/utils/pub/io.dart
@@ -284,11 +284,13 @@ String relativeToPub(String target) {
 
 /// A sink that writes to standard output. Errors piped to this stream will be
 /// surfaced to the top-level error handler.
-final EventSink<List<int>> stdoutSink = stdout;
+// TODO: Unrequired wrapper, stdout is now an EventSink<List<int>>.
+final EventSink<List<int>> stdoutSink = _wrapStdio(stdout, "stdout");
 
 /// A sink that writes to standard error. Errors piped to this stream will be
 /// surfaced to the top-level error handler.
-final EventSink<List<int>> stderrSink = stderr;
+// TODO: Unrequired wrapper, stdout is now an EventSink<List<int>>.
+final EventSink<List<int>> stderrSink = _wrapStdio(stderr, "stderr");
 
 /// Wrap the standard output or error [stream] in a [EventSink]. Any errors are
 /// logged, and then the program is terminated. [name] is used for debugging.