Mash cleanup: remove LoginScreenController::Observer

The two remaining methods are moved to LoginScreenModel::Observer. The
associated methods on mojom::LoginScreen are moved to LoginScreenModel.

Ownership of LoginDataDispatcher is moved to LoginScreenController
because the methods must be callable regardless of the presence of
LockScreen.

Bug: 958206
Change-Id: I0128e8c2bed5ad1f2569318933520e9c89d8b7c1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1626535
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663249}
41 files changed