Refactor Nigori-related error handling

No behavioral changes: we extend or refactor signatures so propagate
Nigori-related errors explicitly.

Bug: 973311
Change-Id: I9a05b87036caf4a15d85b8cce02e7ee510766d7f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1660490
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672482}
10 files changed