Implements WebHistoryServiceFactory on iOS

Implements WebHistoryServiceFactory on iOS

Cleanup iOS BrowserStateKeyedService factories to follow style guide and to
fix typos in the factory description comments.

BUG=429756
Committed: https://crrev.com/cacc7b509a6ab9111b15ff5abc16bdd0de27d15b
Cr-Commit-Position: refs/heads/master@{#337633}

[sdefresne, 2015-07-07 17:08:42]

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

[sdefresne, 2015-07-07 17:08:43]

Please take a look.

[droger, 2015-07-07 17:17:16]

lgtm

[sdefresne, 2015-07-07 17:30:55]

The CQ bit was checked by sdefresne@chromium.org

[sdefresne, 2015-07-07 17:30:56]

The patchset sent to the CQ was uploaded after l-g-t-m from droger@chromium.org
Link to the patchset: https://codereview.chromium.org/1222013005/#ps20001
(title: "Rebase")

[commit-bot: I haz the power, 2015-07-07 17:32:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1222013005/20001

[commit-bot: I haz the power, 2015-07-07 17:39:21]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-07-07 17:40:19]

Patchset 2 (id:??) landed as
https://crrev.com/cacc7b509a6ab9111b15ff5abc16bdd0de27d15b
Cr-Commit-Position: refs/heads/master@{#337633}