Fix crash from ipc_fuzzer

Fix crash from ipc_fuzzer

Can't reproduce original crash so I just fix all crashes I see.

Use WeakPtr in AskUserForSettings callback.

Move chrome::ShowMessageBox in separate task and protection against nested message boxes.

Add missing return into AskUserForSettings.

BUG=472146
Committed: https://crrev.com/442258da866dda0b7ddcb35c51b9591e17c0de8c
Cr-Commit-Position: refs/heads/master@{#324746}

[Vitaly Buka (NO REVIEWS), 2015-04-10 23:25:30]

vitalybuka@chromium.org changed reviewers:
+ alekseys@chromium.org

[Aleksey Shlyapnikov, 2015-04-10 23:55:31]

lgtm

https://codereview.chromium.org/1083433003/diff/20001/printing/printing_conte...
File printing/printing_context_system_dialog_win.cc (right):

https://codereview.chromium.org/1083433003/diff/20001/printing/printing_conte...
printing/printing_context_system_dialog_win.cc:71: return callback.Run(FAILED);
Looks weird to return like this from void function.

[Vitaly Buka (NO REVIEWS), 2015-04-11 00:23:05]

https://codereview.chromium.org/1083433003/diff/20001/printing/printing_conte...
File printing/printing_context_system_dialog_win.cc (right):

https://codereview.chromium.org/1083433003/diff/20001/printing/printing_conte...
printing/printing_context_system_dialog_win.cc:71: return callback.Run(FAILED);
On 2015/04/10 23:55:31, Aleksey Shlyapnikov wrote:
> Looks weird to return like this from void function.

Done.

[Vitaly Buka (NO REVIEWS), 2015-04-11 00:23:08]

The CQ bit was checked by vitalybuka@chromium.org

[Vitaly Buka (NO REVIEWS), 2015-04-11 00:23:08]

The patchset sent to the CQ was uploaded after l-g-t-m from
alekseys@chromium.org
Link to the patchset: https://codereview.chromium.org/1083433003/#ps60001
(title: "Fri Apr 10 17:22:28 PDT 2015")

[commit-bot: I haz the power, 2015-04-11 00:24:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1083433003/60001

[commit-bot: I haz the power, 2015-04-11 01:46:55]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2015-04-11 01:48:35]

Patchset 4 (id:??) landed as
https://crrev.com/442258da866dda0b7ddcb35c51b9591e17c0de8c
Cr-Commit-Position: refs/heads/master@{#324746}