Yet I cannot delete AutomationProxyForExternalTab because it is used by extension_uitest.cc.
Enable some tests meanwhile - now they should be stable enough.

BUG=18797,24664
TEST=ui_tests ok
Review URL: http://codereview.chromium.org/339009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@31016 0039d316-1c4b-4281-b951-d872f2087c98