LatLng constructor
Implementation
LatLng(this._latitude, this._longitude) {
DartValidate.inclusiveBetween(-90.0, 90.0, _latitude,
"Latitude must be between -90 and 90 degrees but was $_latitude");
DartValidate.inclusiveBetween(-180.0, 180.0, _longitude,
"Longitude must be between -90 and 90 degrees but was $_longitude");
}