GitLab

This adds the necessary strings and constants for the three IPH that
will be shown for Tab Groups. It also adds a utility class to facilitate
showing the IPH. Also adds a string for context menu changes.

BUG=930970,930965

Change-Id: Ide45f0a89a66bdab0096213ec8676303df37efe4
Reviewed-on: https://chromium-review.googlesource.com/c/1482592Reviewed-by: David Trainor <dtrainor@chromium.org>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Commit-Queue: Yusuf Ozuysal <yusufo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634819}