Remove Notification::small_image_url_ as it has no users.

Remove Notification::small_image_url_ as it has no users.

Also removes two methods from Notification which only forward calls
to the delegate, and have a single call-site.

BUG=

Committed: https://crrev.com/4542ea08cfd1c978f8e3ec27d797e0945aba0cf1
Cr-Commit-Position: refs/heads/master@{#295499}

[Peter Beverloo, 2014-09-18 13:54:55]

peter@chromium.org changed reviewers:
+ dewittj@chromium.org, mukai@chromium.org

[Peter Beverloo, 2014-09-18 13:54:55]

Very small clean-up patch, but trimming down Notification as far as we can is a
good thing :-).

[Jun Mukai, 2014-09-18 17:40:29]

lgtm

[Peter Beverloo, 2014-09-18 17:41:26]

The CQ bit was checked by peter@chromium.org

[commit-bot: I haz the power, 2014-09-18 17:42:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/574273003/40001

[commit-bot: I haz the power, 2014-09-18 18:18:51]

Committed patchset #3 (id:40001) as 670c44358ccb68bdf7e1fdcd1d1d52c79f5c7acd

[commit-bot: I haz the power, 2014-09-18 18:19:27]

Patchset 3 (id:??) landed as
https://crrev.com/4542ea08cfd1c978f8e3ec27d797e0945aba0cf1
Cr-Commit-Position: refs/heads/master@{#295499}