Adding webview tests to app_shell_browsertest.

Adding webview tests to app_shell_browsertest.

This CL adds the following tests to app_shell_browsertest:
- TestDialogAlert
- TestDialogConfirm
- TestDialogConfirmCancel
- TestDialogConfirmDefaultCancel
- TestDialogConfirmDefaultGCCancel
- TestDialogPrompt

Also, makes sure that we call content::BrowserTestBase::SetUpCommandLine(...) from AppShellTest.

BUG=352293
Committed: https://crrev.com/19132ce1ce87227133c1f1da5ca027a1bda9f5e2
Cr-Commit-Position: refs/heads/master@{#299121}

[lfg, 2014-10-08 22:30:53]

lfg@chromium.org changed reviewers:
+ lazyboy@chromium.org, yoz@chromium.org

[lfg, 2014-10-08 22:30:54]

lazyboy@chromium.org: Please review changes in 

*web_view*

yoz@chromium.org: Please review changes in 

extensions/*

[Yoyo Zhou, 2014-10-08 22:36:52]

LGTM

[lazyboy, 2014-10-08 23:23:51]

lgtm

[lfg, 2014-10-09 15:07:35]

The CQ bit was checked by lfg@chromium.org

[commit-bot: I haz the power, 2014-10-09 15:08:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/634403003/1

[lfg, 2014-10-09 22:16:36]

The CQ bit was unchecked by lfg@chromium.org

[lfg, 2014-10-10 15:18:24]

The CQ bit was checked by lfg@chromium.org

[commit-bot: I haz the power, 2014-10-10 15:19:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/634403003/80001

[commit-bot: I haz the power, 2014-10-10 15:46:30]

Committed patchset #2 (id:80001)

[commit-bot: I haz the power, 2014-10-10 15:50:25]

Patchset 2 (id:??) landed as
https://crrev.com/19132ce1ce87227133c1f1da5ca027a1bda9f5e2
Cr-Commit-Position: refs/heads/master@{#299121}