Start calling show/hide onStart/onStop in DocumentActivity

Start calling show/hide onStart/onStop in DocumentActivity

This logic in documents diverge from CHromeActivity behavior for
archaic reasons (crbug.com/451672). Making documents show/hide
in the same time as all other ChromeActivities with this change.
Verified that the previous bug that caused the bheavior divergence
no longer exists after this CL.

BUG=546182
Committed: https://crrev.com/e548d4580bbd915716a855f9195b6f5f2d63d2a1
Cr-Commit-Position: refs/heads/master@{#360581}

[Yusuf, 2015-11-19 01:09:24]

The CQ bit was checked by yusufo@chromium.org to run a CQ dry run

[Yusuf, 2015-11-19 01:09:33]

yusufo@chromium.org changed reviewers:
+ dfalcantara@chromium.org

[commit-bot: I haz the power, 2015-11-19 01:11:04]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1455343002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1455343002/1

[gone, 2015-11-19 01:26:02]

lgtm

[commit-bot: I haz the power, 2015-11-19 02:32:21]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-11-19 02:32:22]

Dry run: This issue passed the CQ dry run.

[Yusuf, 2015-11-19 15:01:21]

The CQ bit was checked by yusufo@chromium.org

[commit-bot: I haz the power, 2015-11-19 15:02:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1455343002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1455343002/1

[commit-bot: I haz the power, 2015-11-19 15:06:24]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-19 15:07:38]

Patchset 1 (id:??) landed as
https://crrev.com/e548d4580bbd915716a855f9195b6f5f2d63d2a1
Cr-Commit-Position: refs/heads/master@{#360581}

[Yusuf, 2015-11-24 00:05:01]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1464313003/ by yusufo@chromium.org.

The reason for reverting is: BUG=559197

This was causing an early tab.show call which made the test think the activity
is in the foreground.

Reverting my CL for now. Will have to figure out a proper way to hide/show to
reland..