You now have to call size() aswell to get it to work properly

setSize only changes the frame size, not the drawing area

boolean once;
void setup(){
size(200,200);

}
void draw(){
if(!once){
frame.setSize(1000,1000);
once=!once;
}
background(0);
}

Use frame.setResizable(true) inside setup(), so that it knows the frame
resize call is legitimate.