Remove WebContents::AddCreatedCallback in webview test.

BUG=277617
R=lazyboy@chromium.org

Review URL: https://codereview.chromium.org/63853003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234547 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234547