Get rid of 'close' on process. It is very easy to use incorrectly and cut off data from your stream…

tests/standalone/io/process_exit_negative_test.dart

Index: tests/standalone/io/process_exit_negative_test.dart
diff --git a/tests/standalone/io/process_exit_negative_test.dart b/tests/standalone/io/process_exit_negative_test.dart
index 0e5e445c84a60e78020e05e596a3cbad54d5234c..caf5cfbcb334a900967f6a2e8f5a153ca37c8e24 100644
--- a/tests/standalone/io/process_exit_negative_test.dart
+++ b/tests/standalone/io/process_exit_negative_test.dart
@@ -13,6 +13,8 @@ void main() {
                             const ["0", "0", "0", "0"]);
   p.onExit = (int s) {
     print(a.toString());  // Should cause a compilation error here.
-    p.close();
   };
+  // Drain stdout and stderr.
+  p.stdout.onData = p.stdout.read;
+  p.stderr.onData = p.stderr.read;
 }