Update createChildFrame in mojo's html_viewer to take sandbox flags

Update createChildFrame in mojo's html_viewer to take sandbox flags.

WebFrameClient::createChildFrame is being updated to take sandbox flags in https://codereview.chromium.org/838903002/, with the goal of replicating them for out-of-process iframes.  This needs to be updated to the new version as well.

BUG=426512
Committed: https://crrev.com/c098f9c489b5b7976834ae538d8b9f0d446a7da5
Cr-Commit-Position: refs/heads/master@{#312296}

[alexmos, 2015-01-16 21:38:50]

alexmos@chromium.org changed reviewers:
+ aa@chromium.org

[alexmos, 2015-01-16 21:38:50]

aa@: could you please review this small CL?

I missed this when doing similar refactoring in
https://codereview.chromium.org/837283003/

[Aaron Boodman, 2015-01-20 19:47:28]

lgtm

[alexmos, 2015-01-20 22:15:00]

The CQ bit was checked by alexmos@chromium.org

[commit-bot: I haz the power, 2015-01-20 22:15:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/821023005/40001

[commit-bot: I haz the power, 2015-01-20 23:07:11]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-01-20 23:08:03]

Patchset 3 (id:??) landed as
https://crrev.com/c098f9c489b5b7976834ae538d8b9f0d446a7da5
Cr-Commit-Position: refs/heads/master@{#312296}