History: Remove check for searchField existence -- it always exists now.

BUG=None
R=sergiu@chromium.org

Review URL: https://codereview.chromium.org/27507007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229335 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229335