Make the TranslateInfoBarDelegate once again use the TranslateUIDelegate.

This is basically a revert of r234759.  I realized that I can simply pass in an
appropriate WebContents* to the TranslateInfoBarDelegate constructor, instead of
waiting until web_contents() will return something non-NULL.  I feel dumb for
not thinking of this sooner.

BUG=62154
TEST=none
R=hajimehoshi@chromium.org, miguelg@chromium.org

Review URL: https://codereview.chromium.org/107303002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239307 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239307