As pointed out in code review [1]:

"This sort of metric tends to be notoriously hard to use, because it biases toward users who flip the state more frequently.  A user who chooses a state once and then never modifies it again will be almost invisible.

I'd recommend instead sampling this state periodically.  For example, you might want to record whether or not the platform UI is enabled each time that a spelling suggestion is offered."

[1] https://codereview.chromium.org/2792233003#msg23