Add a Mac Lion Performance bot.

Add a Mac Lion Performance bot.
https://bugs.webkit.org/show_bug.cgi?id=77765

Reviewed by Adam Roben.

This will update the master configuration in the following ways:
    Add a new performance slave (apple-xseve-11)
    Add a new Factory to download a build and run perf tests.

* BuildSlaveSupport/build.webkit.org-config/config.json:
* BuildSlaveSupport/build.webkit.org-config/master.cfg:
(DownloadAndPerfTestFactory):
(DownloadAndPerfTestFactory.__init__):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@106703 268f45cc-cd09-0410-ab3c-d52691b4dbfc