mojo api for view based lockscreen.

BUG=721524

Review-Url: https://codereview.chromium.org/2876673002
Cr-Commit-Position: refs/heads/master@{#472966}

• ash/BUILD.gn[diff]
• ash/login/DEPS[Added - diff]
• ash/login/lock_screen_controller.cc[Added - diff]
• ash/login/lock_screen_controller.h[Added - diff]
• ash/login/lock_screen_controller_unittest.cc[Added - diff]
• ash/login/ui/lock_contents_view.cc[diff]
• ash/mojo_interface_factory.cc[diff]
• ash/mus/DEPS[diff]
• ash/mus/manifest.json[diff]
• ash/mus/window_manager_application.cc[diff]
• ash/public/interfaces/BUILD.gn[diff]
• ash/public/interfaces/lock_screen.mojom[Added - diff]
• ash/shell.cc[diff]
• ash/shell.h[diff]
• ash/test/DEPS[diff]
• ash/test/ash_test_helper.cc[diff]
• chrome/browser/chromeos/login/lock/screen_locker.cc[diff]
• chrome/browser/ui/BUILD.gn[diff]
• chrome/browser/ui/ash/lock_screen_client.cc[Added - diff]
• chrome/browser/ui/ash/lock_screen_client.h[Added - diff]
• chrome/browser/ui/views/ash/chrome_browser_main_extra_parts_ash.cc[diff]
• chrome/browser/ui/views/ash/chrome_browser_main_extra_parts_ash.h[diff]