Revert "Remove aura and make a pure mojo::View version of the aura::Window FocusController."

This reverts commit bb29e4293b6e60ee721b5be17f9fa9f4989a1981.

This is a speculative revert due to android waterfall bots failing.

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

Review URL: https://codereview.chromium.org/718573002