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}

• ash/BUILD.gn[diff]
• ash/login/login_screen_controller.cc[diff]
• ash/login/login_screen_controller.h[diff]
• ash/login/login_screen_controller_observer.cc[Deleted - diff]
• ash/login/login_screen_controller_observer.h[Deleted - diff]
• ash/login/ui/lock_contents_view.cc[diff]
• ash/login/ui/lock_contents_view.h[diff]
• ash/login/ui/lock_contents_view_unittest.cc[diff]
• ash/login/ui/lock_debug_view.cc[diff]
• ash/login/ui/lock_debug_view.h[diff]
• ash/login/ui/lock_screen.cc[diff]
• ash/login/ui/lock_screen.h[diff]
• ash/login/ui/lock_screen_sanity_unittest.cc[diff]
• ash/login/ui/login_data_dispatcher.cc[diff]
• ash/login/ui/login_data_dispatcher.h[diff]
• ash/login/ui/login_detachable_base_model.cc[diff]
• ash/login/ui/login_detachable_base_model.h[diff]
• ash/login/ui/login_test_base.cc[diff]
• ash/public/cpp/login_screen_model.h[diff]
• ash/public/cpp/login_types.h[diff]
• ash/public/interfaces/login_screen.mojom[diff]
• ash/shelf/login_shelf_view.cc[diff]
• ash/shelf/login_shelf_view.h[diff]
• ash/shelf/login_shelf_view_unittest.cc[diff]
• chrome/browser/chromeos/login/lock/views_screen_locker.cc[diff]
• chrome/browser/chromeos/login/ui/fake_login_display_host.cc[diff]
• chrome/browser/chromeos/login/ui/fake_login_display_host.h[diff]
• chrome/browser/chromeos/login/ui/login_display_host.h[diff]
• chrome/browser/chromeos/login/ui/login_display_host_mojo.cc[diff]
• chrome/browser/chromeos/login/ui/login_display_host_mojo.h[diff]
• chrome/browser/chromeos/login/ui/login_display_host_webui.cc[diff]
• chrome/browser/chromeos/login/ui/login_display_host_webui.h[diff]
• chrome/browser/chromeos/login/ui/mock_login_display_host.h[diff]
• chrome/browser/chromeos/login/ui/oobe_ui_dialog_delegate.cc[diff]
• chrome/browser/chromeos/login/ui/oobe_ui_dialog_delegate.h[diff]
• chrome/browser/ui/ash/login_screen_client.cc[diff]
• chrome/browser/ui/ash/test_login_screen.cc[diff]
• chrome/browser/ui/ash/test_login_screen.h[diff]
• chrome/browser/ui/ash/test_login_screen_model.cc[diff]
• chrome/browser/ui/ash/test_login_screen_model.h[diff]
• chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.cc[diff]