Change the content settings bubble so that radio buttons are enabled and the correct button is selected by default when an unrecognized plugin is blocked (now happens by default).

BUG=309987

Review URL: https://codereview.chromium.org/37773003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231170 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 231170