Mac: Don't update prefs file unnecessarily when activating windows.

Mac: Don't update prefs file unnecessarily when activating windows.

When activating Chrome app from another app, often times we are reactivating
the same browser window. In this case, we don't need to update prefs with
a new profile and window position. Avoiding prefs update is good because it
triggers JSON file writing to disk (after a 10 seconds delay).

BUG=482027
Committed: https://crrev.com/d47c029d28e6fa926ae2331b4a6b65ccca8b82a6
Cr-Commit-Position: refs/heads/master@{#327418}

[Andre, 2015-04-28 20:16:51]

andresantoso@chromium.org changed reviewers:
+ ccameron@chromium.org

[Andre, 2015-04-28 20:16:51]

ccameron PTAL

[ccameron, 2015-04-28 21:29:18]

lgtm

[Andre, 2015-04-28 21:29:42]

The CQ bit was checked by andresantoso@chromium.org

[Andre, 2015-04-28 21:30:08]

The CQ bit was unchecked by andresantoso@chromium.org

[Andre, 2015-04-28 23:46:01]

The CQ bit was checked by andresantoso@chromium.org

[commit-bot: I haz the power, 2015-04-28 23:46:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1105423003/1

[commit-bot: I haz the power, 2015-04-29 02:13:06]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-29 02:13:47]

Patchset 1 (id:??) landed as
https://crrev.com/d47c029d28e6fa926ae2331b4a6b65ccca8b82a6
Cr-Commit-Position: refs/heads/master@{#327418}