type predicate-ness lost when using Function.prototype.bind

<!-- Please try to reproduce the issue with `typescript@next`. It may have already been fixed. --> **TypeScript Version:** 3.2.4 or @next as of 2019-01-22 <!-- Search terms you tried before logging this (so others can find this issue more easily) --> **Search Terms:** **Code** ```ts const isArray: typeof Array.isArray = Array.isArray.bind(Array); ``` **Expected behavior:** Compiles. **Actual behavior:** Error message: ```ts error TS2322: Type '(arg: any) => boolean' is not assignable to type '(arg: any) => arg is any[]'. Signature '(arg: any): boolean' must be a type predicate. ``` What seems to be happening is that the type predicate-ness of Array.isArray is lost when .bind is used. I tested with a few type predicate functions, and always get the same error. **Playground Link:** Not reproducible on playground, because it depends on a higher TS version. [In the playground](https://www.typescriptlang.org/play/index.html#src=%0D%0Aconst%20isArray%20%3D%20Array.isArray.bind(Array)%3B%0D%0A%0D%0A%0D%0A%0D%0A), the type of the RHS is `any`, so there is no compilation error. **Related Issues:** - Typings for `Function.prototype.bind` were discussed in https://github.com/Microsoft/TypeScript/issues/212 but I couldn't find any mention of type predicates. - [Discussion on StackOverflow](https://stackoverflow.com/questions/54316578/type-predicate-ness-lost-when-using-function-prototype-bind?noredirect=1#comment95453581_54316578)