[ios] Add password generation manual fallback action

Bug: 886583
Change-Id: I29f7ac59c8fb29888d85031db459296f2ed87eeb
Reviewed-on: https://chromium-review.googlesource.com/c/1378138
Reviewed-by: Vadym Doroshenko <dvadym@chromium.org>
Reviewed-by: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Commit-Queue: David Jean <djean@chromium.org>
Cr-Commit-Position: refs/heads/master@{#617816}
8 files changed