Change ScheduledProcess's output streams over to be ScheduledStreams.

sdk/lib/_internal/pub/test/real_version_test.dart

Index: sdk/lib/_internal/pub/test/real_version_test.dart
diff --git a/sdk/lib/_internal/pub/test/real_version_test.dart b/sdk/lib/_internal/pub/test/real_version_test.dart
index 75f1a22deb60cca6c8f7b249078755d36c0fbc4c..97138087de49fe4b209f9b55f545314187429aa6 100644
--- a/sdk/lib/_internal/pub/test/real_version_test.dart
+++ b/sdk/lib/_internal/pub/test/real_version_test.dart
@@ -33,7 +33,7 @@ main() {
         Platform.operatingSystem == "windows" ? "pub.bat" : "pub");
 
     var pub = new ScheduledProcess.start(pubPath, ['version']);
-    expect(pub.nextLine(), completion(startsWith("Pub")));
+    pub.stdout.expect(startsWith("Pub"));
     pub.shouldExit(exit_codes.SUCCESS);
   });
 }