Initialize variations seed fetching via OnAppEnterForeground.

Initialize variations seed fetching via OnAppEnterForeground.

On Android, instead of calling StartRepeatedVariationsSeedFetch()
in chrome_browser_main.cc, this changes the code to instead have
that be called by the first call to OnAppEnterForeground().

This will allow (in a future change) to have the caller of
OnAppEnterForeground() to first set the restrict mode param,
before fetching gets initialized. (Otherwise, fetching was
being initialized too early before the param could be set.)

BUG=452605
Committed: https://crrev.com/391ece3aa22ebad761a63628dd10dfdef9028f7b
Cr-Commit-Position: refs/heads/master@{#313746}

[Alexei Svitkine (slow), 2015-01-28 20:37:59]

Patchset #1 (id:1) has been deleted

[Alexei Svitkine (slow), 2015-01-28 20:38:20]

asvitkine@chromium.org changed reviewers:
+ jwd@chromium.org, rkaplow@chromium.org

[jwd, 2015-01-29 15:37:25]

lgtm

[rkaplow, 2015-01-29 15:46:43]

lgtm

[rkaplow, 2015-01-29 15:46:44]

lgtm

[Alexei Svitkine (slow), 2015-01-29 15:49:09]

asvitkine@chromium.org changed reviewers:
+ sky@chromium.org

[Alexei Svitkine (slow), 2015-01-29 15:49:10]

+sky for chrome/browser owners

[sky, 2015-01-29 17:42:08]

LGTM

[Alexei Svitkine (slow), 2015-01-29 18:01:06]

The CQ bit was checked by asvitkine@chromium.org

[commit-bot: I haz the power, 2015-01-29 18:02:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/880263005/20001

[commit-bot: I haz the power, 2015-01-29 18:44:00]

Committed patchset #1 (id:20001)

[commit-bot: I haz the power, 2015-01-29 18:44:57]

Patchset 1 (id:??) landed as
https://crrev.com/391ece3aa22ebad761a63628dd10dfdef9028f7b
Cr-Commit-Position: refs/heads/master@{#313746}