...the implementation in ChartView.cxx oddly got removed from
<https://gerrit.libreoffice.org/#/c/14431/1> to
<https://gerrit.libreoffice.org/#/c/14431/2>, but the declaration in
chartcore.component was missing from the start

Change-Id: I71699ee74278f7e419eca63c5784b46efc42d96b