Reland "cros: Move most event/widget handling logic out of LoginBubble"

This reverts commit bb9ca465cac1a3ec4d0670844865b40efb003c11.

Bug: 912658
Change-Id: I978c067d22486f58011e4025d9913100057c8a93
Reviewed-on: https://chromium-review.googlesource.com/c/1368645
Commit-Queue: Quan Nguyen <qnnguyen@chromium.org>
Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615314}
5 files changed