Fix serialization of expected outcomes in test driver.

The outcomes are saved as a set and need to be converted into
a list to be json-serializable.

TBR=tandrii@chromium.org

Review URL: https://codereview.chromium.org/710073002

Cr-Commit-Position: refs/heads/master@{#25246}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25246 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

tools/testrunner/local/progress.py

@@ -333,7 +333,7 @@ class JsonTestProgressIndicator(ProgressIndicator):
       "stderr": test.output.stderr,
       "exit_code": test.output.exit_code,
       "result": test.suite.GetOutcome(test),
-      "expected": test.outcomes or ["PASS"],
+      "expected": list(test.outcomes) or ["PASS"],
     })