Update ChromePasswordManagerClient::GetPasswordManager

ChromePasswordManagerClient::GetPasswordManager returns PasswordManager*
instead of PasswordManagerInterface*. It's problematic as tests aren't
able to mock PasswordManager. This CL fixes and makes necessary changes
to accommodate this transition.

Change-Id: Ia5b0e61a3afaf041bd4ec66632aaa5bf61cdbe0b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6172450
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Commit-Queue: Viktor Semeniuk <vsemeniuk@google.com>
Cr-Commit-Position: refs/heads/main@{#1405540}