Add executable to Options interface to get the name of the executable used to execute the script.

tests/standalone/io/process_run_output_test.dart

Index: tests/standalone/io/process_run_output_test.dart
diff --git a/tests/standalone/io/process_run_output_test.dart b/tests/standalone/io/process_run_output_test.dart
index 5d78af29cbd3ebe9d0c1c9a86de775e0684c555f..c0e1796cea07237df2b8c852b3caa63ce8d35367 100644
--- a/tests/standalone/io/process_run_output_test.dart
+++ b/tests/standalone/io/process_run_output_test.dart
@@ -31,7 +31,7 @@ test(scriptFile, encoding, stream) {
   var options = new ProcessOptions();
   if (stream == 'stdout') {
     options.stdoutEncoding = enc;
-    new Process.run(getDartFileName(), [scriptFile, encoding, stream],
+    new Process.run(new Options().executable, [scriptFile, encoding, stream],
                     options, (exit, out, err) {
       Expect.equals(exit, 0);
       Expect.equals(err, '');
@@ -39,7 +39,7 @@ test(scriptFile, encoding, stream) {
     });
   } else {
     options.stderrEncoding = enc;
-    new Process.run(getDartFileName(), [scriptFile, encoding, stream],
+    new Process.run(new Options().executable, [scriptFile, encoding, stream],
                     options, (exit, out, err) {
       Expect.equals(exit, 0);
       Expect.equals(out, '');