arc method Null safety
Implementation
void arc(num x, num y, num radius, num startAngle, num endAngle,
[bool anticlockwise = false]) {
// TODO(terry): This should not be needed: dartbug.com/20939.
JS('void', '#.arc(#, #, #, #, #, #)', this, x, y, radius, startAngle,
endAngle, anticlockwise);
}