Invalidate TKO tests only when necessary.

Before running expensive UPDATE queries, check the invalidation
statuses of TKO tests and issue a query only when needed.

BUG=chromium:733103
TEST=bin/run_tests && bin/run_yapf -i && bin/run_lint

Change-Id: I621a0874ae1d8b020723015f7cd4e336aec35e3e
Reviewed-on: https://chromium-review.googlesource.com/708098
Commit-Ready: Shuhei Takahashi <nya@chromium.org>
Tested-by: Shuhei Takahashi <nya@chromium.org>
Reviewed-by: Prathmesh Prabhu <pprabhu@chromium.org>
4 files changed