Fix and re-enable a test I broke with the find bar changes I made last night.

Remove Browser::find_bar(), make everyone use either Browser::GetFindBarController() which creates the FindBarController on demand, or a new method HasFindBarController(), which can be used to check for its existence (so as to avoid creating it unnecessarily).

http://crbug.com/26231
TEST=interactive ui tests, standard find tests

Review URL: http://codereview.chromium.org/348015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@30507 0039d316-1c4b-4281-b951-d872f2087c98