UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/57.0.2987.98 Safari/537.36

Steps to reproduce the problem:
1. open Chome Dev Tools -> Console
2. var params = new URLSearchParams({key: "test"})
3. params.toString()
4.  it returns `%5Bobject+Object%5D=`

What is the expected behavior?
According to the spec, the URLSearchParams.toString() method should return `key=test`. Firefox correctly does this. However, Chrome 57 returns `%5Bobject+Object%5D=`

What went wrong?
I believe that when instantiating a URLSearchParams object, it's not properly parsing the object argument, which results in a malformed value being set. The problem is cascaded when trying to get or confirm a particular key by utilizing .get('key') or .has('key'), respectively. They return undefined.

Did this work before? N/A 

Chrome version: 57.0.2987.98  Channel: stable
OS Version: OS X 10.12.3
Flash Version: