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This CL creates the skeleton of common password controller and moves FormActivityObserver related logic into it`.
The goal is to move common password autofill logics into components folder so that they can be shared by both Chrome iOS and //ios/web_view.

> Moved webState and jsPasswordManager into helper class.
> Moved FormActivityObserver logic into helper class.

Bug: 865114
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I2dbfdb1cb4f0bdf22bf1d5c37451f46682addcac
Reviewed-on: https://chromium-review.googlesource.com/1156528Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Reviewed-by: Hiroshi Ichikawa <ichikawa@chromium.org>
Reviewed-by: John Wu <jzw@chromium.org>
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Commit-Queue: Scott Wu <scottwu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585356}