webui: Do not set 'toolkit' property for webui.

webui: Do not set 'toolkit' property for webui.

The 'toolkit' property is no longer used by webui pages. So do not set it
anymore for views. Also, remove associated functions for detecting gtk.

BUG=500004
Committed: https://crrev.com/37c71fc16baac96ffc19e39e4a112cdae4e295da
Cr-Commit-Position: refs/heads/master@{#334888}

[sadrul, 2015-06-16 14:28:14]

sadrul@chromium.org changed reviewers:
+ estade@chromium.org

[sadrul, 2015-06-16 19:55:58]

sadrul@chromium.org changed reviewers:
+ jhawkins@chromium.org
- estade@chromium.org

[sadrul, 2015-06-16 19:55:59]

+jhawkins@ instead since estade@ is OOO

[James Hawkins, 2015-06-17 17:58:40]

lgtm

[sadrul, 2015-06-17 19:11:20]

The CQ bit was checked by sadrul@chromium.org

[commit-bot: I haz the power, 2015-06-17 19:12:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1185363002/1

[commit-bot: I haz the power, 2015-06-17 19:18:18]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-17 19:19:19]

Patchset 1 (id:??) landed as
https://crrev.com/37c71fc16baac96ffc19e39e4a112cdae4e295da
Cr-Commit-Position: refs/heads/master@{#334888}