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This has several benefits:
1) No longer generating the authentication token for each benchmark results
too early. Before this CL, we generate authentication for every benchmark
results first, then process each perf results & upload them. With such logic,
the last benchmark to be uploaded may have token generated for a long period of
time.
2) Enables generating a new token for every retry attempt in
core/results_dashboard.py.

Bug:864565
Cq-Include-Trybots: master.tryserver.chromium.perf:obbs_fyi
Change-Id: I8b2d681efdaa241a8af19a7ffbf126523caa12a9

NOTRY=true # CQ flakes

Change-Id: I8b2d681efdaa241a8af19a7ffbf126523caa12a9
Reviewed-on: https://chromium-review.googlesource.com/1150080
Commit-Queue: Ned Nguyen <nednguyen@google.com>
Reviewed-by: Simon Hatch <simonhatch@chromium.org>
Reviewed-by: Juan Antonio Navarro Pérez <perezju@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577916}