UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_4) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/11.1 Safari/605.1.15

Steps to reproduce the problem:
1. Open the Task Manager so that you can see how much CPU is used by each tab.
2. Open the Dev Tools in a tab.
3. In the console, type the following, to trigger a synchronous AJAX call:

function reqListener () {
  console.log(this.responseText);
}

var oReq = new XMLHttpRequest();
oReq.addEventListener("load", reqListener);
oReq.open("GET", "http://www.example.org/example.txt", false);
oReq.send();

4. Note that the CPU consumption of that tab jumps to about 100%, as reported by the Task Manager.

What is the expected behavior?
Synchronous AJAX calls are rightly deprecated, as they can cause the browser to lock up. But the CPU is not expected to go to 100% and stay there.

What went wrong?
The Google Chrome Helper process seems to get stuck in a loop following a synchronous AJAX call. It remains in this state as long as that browser tab is open, even if you navigate away.

Did this work before? Yes Either 65 or 66

Does this work in other browsers? Yes

Chrome version: 67.0.3396.62  Channel: stable
OS Version: OS X 10.13.4
Flash Version: 

The use of the synchronous AJAX call is occurring only in my development environment; it fetches javascript files that are not collated into a single file. So it's not a production problem. However, it remains very annoying.