Fix platform picker change handler in garden-o-matic

Fix platform picker change handler in garden-o-matic
https://bugs.webkit.org/show_bug.cgi?id=90010

Reviewed by Simon Fraser.

* BuildSlaveSupport/build.webkit.org-config/public_html/TestFailures/scripts/ui.js:
The old code never worked. This is hard to test because change handlers require
a user-initiated action and the code is changing the window's location, which would
navigate the test page.

* BuildSlaveSupport/build.webkit.org-config/public_html/TestFailures/styles/onebar.css:
Fix the CSS so it doesn't cause the tabstrip to be disconnected from the tabs on Linux
due to the large margin-bottom.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@121287 268f45cc-cd09-0410-ab3c-d52691b4dbfc