Disable SystemMonitor.* in base_unittests.

This should green the tree and is only a temporary workaround.

http://crbug.com/12187

TBR=nsylvain

Review URL: http://codereview.chromium.org/113542

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@16308 0039d316-1c4b-4281-b951-d872f2087c98