Object spread fails to type check

Given

```js
/** @param {{x: number, y: string}} x */
function f(x) {}

/** @type {{y: string}} */
const o = {y: "a"};

f({x: 1, ...o})
```

https://closure-compiler.appspot.com/home#code%3D%252F%252F%2520%253D%253DClosureCompiler%253D%253D%250A%252F%252F%2520%2540compilation_level%2520ADVANCED_OPTIMIZATIONS%250A%252F%252F%2520%2540output_file_name%2520default.js%250A%252F%252F%2520%2540formatting%2520pretty_print%250A%252F%252F%2520%253D%253D%252FClosureCompiler%253D%253D%250A%250A%250A%252F**%2520%2540param%2520%257B%257Bx%253A%2520number%252C%2520y%253A%2520string%257D%257D%2520x%2520*%252F%250Afunction%2520f(x)%2520%257B%257D%250A%250A%252F**%2520%2540type%2520%257B%257By%253A%2520string%257D%257D%2520*%252F%250Aconst%2520o%2520%253D%2520%257By%253A%2520%2522a%2522%257D%253B%250A%250Af(%257Bx%253A%25201%252C%2520...o%257D)

I'm getting a type error. I assume this is just because object spread is not fully implemented yet?