Flip Horizontal

I would like to see the "Flip Horizontal" feature for layers upgraded.

At this point all it does, it goes to scale property of selected layer, uncheckes the constrain proportions and puts minus in front of the number in horizontal dimension. 

Which works, if there are no keyframes already in the scale property.

If there are keyframes already present, the function just creates a new keyframe at the time where time indicator currently is and flips that one keyframe and doesnt touch any other keyframe, which results in distorted, rotating layer, rather than flipped layer.

So my suggestion would be, that the function would first check if there are any scale keyframes already present and if yes, it would flip all the keyframes already present without creating a new one.