I have been using yaris for more than 1 year and I never experienced such behavior of the steering while breaking. I once had to apply emergency brake at around 60 km/h and my car didn't go out of control thanks to God.
Test your alignment by cruising on an even road and taking your hands off the steering, if the car leans to one side, then the alignment needs to be corrected.
However, you should test your car's braking system so that you can control it in an emergency situation.