[ios] add FormData extraction api to password form helper

And unit test.

Bug: 886583
Change-Id: Icbcf6d965b49698a99b1637c3b3e8954a03149d8
Reviewed-on: https://chromium-review.googlesource.com/c/1477901
Reviewed-by: Vadym Doroshenko <dvadym@chromium.org>
Commit-Queue: David Jean <djean@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634129}
3 files changed