Introducing NavigationSimulator back/forward

Added capability to NavigationSimulator to do back and forward
navigations. Also modified some unit tests that were using it.

Bug: 728571
Change-Id: I6ef5a6609543b90ec9309be1830c866d04f0fa3d
Reviewed-on: https://chromium-review.googlesource.com/647539
Commit-Queue: Arthur Hemery <ahemery@chromium.org>
Reviewed-by: Charlie Reis <creis@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Reviewed-by: Jialiu Lin <jialiul@chromium.org>
Reviewed-by: Camille Lamy <clamy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520053}
5 files changed