Update HandleValidationTimeout to reflect that inflight_statuses is a set.
Update HandleValidationTimeout to reflect that inflight_statuses is a set.

CL:174891 changed inflight_statuses to be a set instead of a dict, but I
forgot to update the HandleValidationTimeout method. Fix this.

BUG=chromium:315419
TEST=Unit tests.

Change-Id: Id9632ec9565c6abacc43e5c9bb19b333d69451b2
Reviewed-on: https://chromium-review.googlesource.com/175848
Reviewed-by: Yu-Ju Hong <52dc720c411f8e2156e608c1a8b894a917489667@chromium.org>
Commit-Queue: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>
Tested-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>

chadversary/chromiumos.chromite,chadversary/chromiumos.chromite,bpsinc-native/src_third_party_chromite,bpsinc-native/src_third_party_chromite,bpsinc-native/src_third_party_chromite