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

Changes made:
- Move the (keyboard/click/tap) event handling logic into a
  LoginBubbleHandler class.
- Move the widget handling into LoginBaseBubbleView itself

Bug: 912658
Change-Id: Ia1a9bf4b8d847ef74ef1716e73dfe1b16b8d19b2
Reviewed-on: https://chromium-review.googlesource.com/c/1366516
Commit-Queue: Quan Nguyen <qnnguyen@chromium.org>
Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614544}
4 files changed