Revert of Disable NavigatorTestWithBrowserSideNavigation.BeginNavigation (patchset...

Revert of Disable NavigatorTestWithBrowserSideNavigation.BeginNavigation (patchset #1 id:1 of https://codereview.chromium.org/905463004/)

Reason for revert:
Test fixed in https://codereview.chromium.org/904673004/, https://crrev.com/315063.

Original issue's description:
> Disable NavigatorTestWithBrowserSideNavigation.BeginNavigation
>
> This test fails within the WebContentsObserverSanityChecker, since no IPC
> for RenderFrameCreated is sent. Disable while we find a good way to make
> the sanity checker play nicely within the unit test framework running in
> --site-per-process
>
> BUG=417518
>
> Committed: https://crrev.com/33e0ed259a19bc6c918fa11fcacffdf709440447
> Cr-Commit-Position: refs/heads/master@{#314960}

TBR=alexmos@chromium.org,jam@chromium.org,nasko@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=417518

Review URL: https://codereview.chromium.org/870653006

Cr-Commit-Position: refs/heads/master@{#315065}