Add methods to SceneOverlay interface
This change adds onBackPressed, onHideLayout, and handlesTabCreating
to the SceneOverlay interface. If any of the SceneOverlays for a
layout claim to handle tab creation, the normal animation will be
skipped.
BUG=
584340
Committed:
https://crrev.com/a4c4b94e33a3b9d16eb5a09a2e2fa227def420ea
Cr-Commit-Position: refs/heads/master@{#387766}