CRhinoDisplayPipeline::MeasureString has no defaults for middle, height and fontface, but its sibling CRhinoDisplayPipeline::DrawString has these defaults. I propose the following:
CRhinoDisplayPipeline::MeasureString(CRect &rect, const wchar_t* text, ON_2dPoint point, bool middle = false, int heightPixels = 12, const wchar_t* fontface = L"Arial")