Fix a style guide violation in KeyedService.

Fix a style guide violation in KeyedService.

According to the style guide [1], constructors and destructor should come
before any other method declaration. Fixes KeyedService method ordering
to follow said guide.

[1]: https://google.github.io/styleguide/cppguide.html#Declaration_Order

BUG=None

Committed: https://crrev.com/e34c4d70f455816654cb51dfacf832db7228b610
Cr-Commit-Position: refs/heads/master@{#360797}

[sdefresne, 2015-11-19 11:46:19]

sdefresne@chromium.org changed reviewers:
+ erg@chromium.org

[sdefresne, 2015-11-19 11:46:20]

As pointed out in
https://codereview.chromium.org/1438043008/diff/360001/components/ntp_snippet...
KeyedService method declaration order was not following the style guide.

Please take a look.

[Elliot Glaysher, 2015-11-19 18:26:42]

lgtm

[sdefresne, 2015-11-19 18:29:02]

The CQ bit was checked by sdefresne@chromium.org

[commit-bot: I haz the power, 2015-11-19 18:29:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1459843002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1459843002/1

[commit-bot: I haz the power, 2015-11-19 18:45:11]

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

[commit-bot: I haz the power, 2015-11-19 18:45:12]

Try jobs failed on following builders:
  linux_android_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_android_r...)

[sdefresne, 2015-11-20 09:57:52]

The CQ bit was checked by sdefresne@chromium.org

[commit-bot: I haz the power, 2015-11-20 09:58:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1459843002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1459843002/1

[commit-bot: I haz the power, 2015-11-20 10:57:08]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-20 10:57:59]

Patchset 1 (id:??) landed as
https://crrev.com/e34c4d70f455816654cb51dfacf832db7228b610
Cr-Commit-Position: refs/heads/master@{#360797}