Fix crash of ExtensionManagement in guest mode

Fix crash of ExtensionManagement in guest mode

The default BrowserContextKeyedServiceFactory::GetBrowserContextToUse() returns NULL for guest mode profile, overriding it to redirect to original profile.

BUG=411763
TBR=finnur@chromium.org

Committed: https://crrev.com/9733df1451a579792b8cb728b51697e03300ae5c
Cr-Commit-Position: refs/heads/master@{#293729}

[binjin, 2014-09-08 11:46:37]

binjin@chromium.org changed reviewers:
+ joaodasilva@chromium.org

[binjin, 2014-09-08 11:46:37]

Joao, PTAL at this fix.

[Joao da Silva, 2014-09-08 13:21:17]

lgtm

[binjin, 2014-09-08 13:31:56]

The CQ bit was checked by binjin@chromium.org

[commit-bot: I haz the power, 2014-09-08 13:32:48]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/binjin@chromium.org/550053003/1

[commit-bot: I haz the power, 2014-09-08 15:24:52]

Committed patchset #1 (id:1) as ee5a24fc3674639596f125f6ef95c785e7acf096

[commit-bot: I haz the power, 2014-09-10 03:46:25]

Patchset 1 (id:??) landed as
https://crrev.com/9733df1451a579792b8cb728b51697e03300ae5c
Cr-Commit-Position: refs/heads/master@{#293729}