Revert a workaround commit for a Use-After-Free crash.

Revert a workaround commit r20158 for a Use-After-Free issue (http://crbug.com/244746) because a cleaner CL r207218 is landed.
URLRequestContext does not inherit SupportsWeakPtr now.

R=mmenke
BUG=244746

Review URL: https://chromiumcodereview.appspot.com/16870008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@207811 0039d316-1c4b-4281-b951-d872f2087c98
  void SetOnStartOpenConnection(
      const base::Callback<int(SocketStreamEvent*)>& callback) {
    on_start_open_connection_ = callback;
  }

  void SetOnStartOpenConnection(
      const base::Callback<int(SocketStreamEvent*)>& callback) {
    on_start_open_connection_ = callback;
  }
