[Cleanup] Add CreateWebContentsWithID helper to TabStripModelTest

[Cleanup] Add CreateWebContentsWithID helper to TabStripModelTest

Since SetID is usually called immediately after CreateWebContents,
this lets you do both at once to improve legibility/conciseness.

Committed: https://crrev.com/d2ba9ec2f1bd12bf49fae11063ed2f79d547dc6d
Cr-Commit-Position: refs/heads/master@{#310441}

[johnme, 2015-01-07 22:50:17]

johnme@chromium.org changed reviewers:
+ sky@chromium.org

[sky, 2015-01-07 23:23:56]

LGTM

[johnme, 2015-01-08 00:50:48]

The CQ bit was checked by johnme@chromium.org

[commit-bot: I haz the power, 2015-01-08 00:51:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/800193006/1

[commit-bot: I haz the power, 2015-01-08 02:09:23]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-08 02:12:24]

Patchset 1 (id:??) landed as
https://crrev.com/d2ba9ec2f1bd12bf49fae11063ed2f79d547dc6d
Cr-Commit-Position: refs/heads/master@{#310441}