Introduce CefColorChooserHandler. Embedders can implement it to display color chooser in their app. If not implemented, or if OnCreateColorSelection returns false, a default implementation is used, the same color picker as chrome is used (based on views toolkit)
limitation of this patch: We only allow one picker to displayed at the time for a given BrowserHost. The alternative would be find a way to specify which color picker is related to OnEndColorSelection and OnCreateColorSelection calls.