In print-stale-test-expectations-entries, avoid repeating the same request.

When running print-stale-test-expectations-entries, I noticed that it makes a request for each line even if it already checked whether a particular bug is stale; this change would speed up print-stale-test-expectations-entries by saving the results of the request about the state of the bug.

BUG=597797

Review-Url: https://codereview.chromium.org/2131463005
Cr-Commit-Position: refs/heads/master@{#404680}
1 file changed