Revert of Disable NavigatorTestWithBrowserSideNavigation.BeginNavigation

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
Committed: https://crrev.com/6d1a88389400427cca73c7c18fb5c178145f2b04
Cr-Commit-Position: refs/heads/master@{#315065}

[Charlie Reis, 2015-02-06 18:02:54]

Created Revert of Disable NavigatorTestWithBrowserSideNavigation.BeginNavigation

[commit-bot: I haz the power, 2015-02-06 18:03:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/870653006/1

[commit-bot: I haz the power, 2015-02-06 18:04:15]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-06 18:05:12]

Patchset 1 (id:??) landed as
https://crrev.com/6d1a88389400427cca73c7c18fb5c178145f2b04
Cr-Commit-Position: refs/heads/master@{#315065}