Convert four tab-related helpers in chrome_earl_grey's to compile under EG2.

This includes:
* openNewTab
* openNewIncognitoTab
* closeAllTabsInCurrentMode
* closeAllIncognitoTabs

All four are similar and fairly routine, so they were combined in this CL.

A small test is added to smoke_egtest to exercise all of them.

Bug: 922813
Change-Id: I3244c1f5ce82b207e68ee5fc80a7eae014f8496b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1622436
Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: ericale <ericale@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661979}
5 files changed