Flow not checking `new C` when `C` is type `Class<...>`

I have this code and I would expect it to throw error; but it doesn't.

````javascript
type Foo = {
constructor(a: number): void;
};

function construct(FooClass: Class) {
const w = new FooClass('this is a string');
}
````

Similarly, this doesn't check errors

````javascript
type Foo = {
constructor(): void;
};

function construct(FooClass: Class>) {
const w: Foo = new FooClass();
}
````

I found no other way to say 'this variable is a class, you can call new() on it, only with the expected parameters, and it makes a new object of that type'. Maybe `Class` is not correct, but then what is; `$Type` and friends doesn't work either.

I am needing this, because I want to write at least somehow correct immutable-js Record typedefs; `var ABRecord = Record({a: 1, b: 2})` doesn't create a new record, but a new class, on which you can call `new ABRecord({})`. I want to capture that.