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- Created SharedPasswordController to share ios specific code without
  being either ios/chrome or ios/web_view specific.
- Move MakeSimpleFormData into test_helpers.
- Make PasswordSuggestionHelper and PasswordFormHelper injected at
  initialization to aid with mocking in unit test.
- Left some TODOs to continue cleanup of shared code in
  //components/password_manager/ios/...

Change-Id: Ia877ecef4cb44d87f069500fbccb1d0f7320a598
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2254351
Commit-Queue: John Wu <jzw@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Reviewed-by: Maria Kazinova <kazinova@google.com>
Cr-Commit-Position: refs/heads/master@{#790517}