Explicitly call OnModelChanged when there are no titles to load

Explicitly call OnModelChanged when there are no titles to load

Fixs several release blocking regressions in the behaviour of the
startup page list. Lamentably there are no tests for this code and
adding new ones looks tricky (we'd either need to fix crbug.com/419370)
or refactor the classes to be testable.

BUG=452370, 452407
Committed: https://crrev.com/ac59daacf5d6dfd47ea67bc6ddd930b499215698
Cr-Commit-Position: refs/heads/master@{#313487}

[alex clarke (OOO till 29th), 2015-01-27 15:28:46]

alexclarke@chromium.org changed reviewers:
+ jochen@chromium.org

[jochen (gone - plz use gerrit), 2015-01-28 11:00:26]

lgtm

[alex clarke (OOO till 29th), 2015-01-28 11:02:01]

The CQ bit was checked by alexclarke@chromium.org

[commit-bot: I haz the power, 2015-01-28 11:03:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/879953002/1

[commit-bot: I haz the power, 2015-01-28 12:07:53]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-28 12:08:59]

Patchset 1 (id:??) landed as
https://crrev.com/ac59daacf5d6dfd47ea67bc6ddd930b499215698
Cr-Commit-Position: refs/heads/master@{#313487}