No compile error thrown when `this` referenced before call to `super` completes

TypeScript Version:

1.8.9

Code
JSFiddle: https://jsfiddle.net/kitsonk/fs9t96ep/
TS Playground: http://goo.gl/X7cgvV

class A {
    constructor(fn: () => void) {
        fn.call(this);
    }
    foo: string = 'foo';
}

class B extends A {
    constructor() {
        super(() => {
            console.log(this);
        });
    }
    bar: string = 'bar';
}

const b = new B();

Expected behavior:
Typescript should guard against the use of this as the call to super has not completed. Thus it should not compile.

Actual behavior:
Typescript compiles this successfully. It works fine when the target is set to es5 but breaks the browser when target is set to es6.
Error is: VM89:55 Uncaught ReferenceError: this is not defined

从 issue 中的 TypeScript 1.8.9 复现开始，使用链接的 TS Playground 或 JSFiddle，并比较以 ES5 和 ES6 为目标时的编译结果。跟踪编译器如何处理传递给 super 的 callback 内部的 this；当无效的 ES6 情况被拒绝，同时有效的构造函数用法仍受支持时，即视为完成。