Change ScheduledProcess's output streams over to be ScheduledStreams.

sdk/lib/_internal/pub/test/hosted/version_negotiation_test.dart

Index: sdk/lib/_internal/pub/test/hosted/version_negotiation_test.dart
diff --git a/sdk/lib/_internal/pub/test/hosted/version_negotiation_test.dart b/sdk/lib/_internal/pub/test/hosted/version_negotiation_test.dart
index 64247ea1b453a9d6d05b2a1c995750a03303b7e5..4be7a4a7275d1d1f8fe1c2056137b07752e4ac77 100644
--- a/sdk/lib/_internal/pub/test/hosted/version_negotiation_test.dart
+++ b/sdk/lib/_internal/pub/test/hosted/version_negotiation_test.dart
@@ -62,9 +62,9 @@ main() {
 
       pub.shouldExit(1);
 
-      expect(pub.remainingStderr(), completion(equals(
+      pub.stderr.expect(emitsLines(
           "Pub 0.1.2+3 is incompatible with the current version of 127.0.0.1.\n"
-          "Upgrade pub to the latest version and try again.")));
+          "Upgrade pub to the latest version and try again."));
     });
   });
 }