Use seneschal SharePathResponse.path rather than generating independently

This is what I should have done in the most recent
crosreview.com/1414253

Bug: 912638
Change-Id: I14abec116ed195333be5b5def5e1638c0f214885
Reviewed-on: https://chromium-review.googlesource.com/c/1424521
Commit-Queue: Nicholas Verne <nverne@chromium.org>
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Reviewed-by: Nicholas Verne <nverne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#624511}
2 files changed