Reland: Remove aura and make a pure mojo::View version of FocusController.

[Changes: Remove additional deps which Linux/Windows was fine with, but
which broke android because it implied an aura dependency. window_manager
should now be properly deauraed.]

This patch is only half done, however the main driver (removing aura) is
needed by other teams for them to make progress.

Input handling is regressed in this patch; while FocusController is
rebuilt to the point where it should theoretically work, all of the
details about ui::EventTargeter don't work correctly. There is an empty
subclass ViewTargeter which will need to be filled out before

Thankfully, this should only regress people who are using the wm_flow
demo, and this should unblock the android guys who don't have aura
support on their platform.

BUG=431047
TBR=eseidel@chromium.org, sky@chromium.org

Review URL: https://codereview.chromium.org/710203006