Make StreamSubscription be the active part of a stream.

runtime/bin/socket_patch.dart

Index: runtime/bin/socket_patch.dart
diff --git a/runtime/bin/socket_patch.dart b/runtime/bin/socket_patch.dart
index 3de4c29597c8148429f16abbd40ccc6adb65e37c..8dbb54b54825362810a09c9e86c135381b6eb664 100644
--- a/runtime/bin/socket_patch.dart
+++ b/runtime/bin/socket_patch.dart
@@ -842,12 +842,6 @@ class _SocketStreamConsumer extends StreamConsumer<List<int>> {
       offset += socket._write(buffer, offset, buffer.length - offset);
       if (offset < buffer.length) {
         if (!paused) {
-          paused = true;
-          // TODO(ajohnsen): It would be nice to avoid this check.
-          // Some info: socket._write can emit an event, if it fails to write.
-          // If the user closes the socket in that event, stop() will be called
-          // before we get a change to pause.
-          if (subscription == null) return;
           subscription.pause();
         }
         socket._enableWriteEvent();