Save and restore tab groups

This implements basic session restore functionality for tab
groups. Currently, only whole browser session restore is supported;
restoring a window or a tab from the history menu won't restore

Bug: 905491
Change-Id: Ib6ad643c7efd75f468bb518fa5881b17a3d9f05f
Reviewed-by: Scott Violet <>
Reviewed-by: Bret Sepulveda <>
Commit-Queue: Collin Baker <>
Cr-Commit-Position: refs/heads/master@{#666500}
22 files changed