UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Ubuntu Chromium/58.0.3029.110 Chrome/58.0.3029.110 Safari/537.36

Steps to reproduce the problem:
1. Register a service worker with a `fetch` event handler
2. Wait for the worker to become active
3. Append a new iframe to the current document (given step 1 and 2, this should
   be controlled by the service worker)
4. Issue a synchronous XHR request from the iframe

What is the expected behavior?
The service worker's `fetch` event should be triggered for the synchronous XHR.

What went wrong?
The service worker's `fetch` event is not triggered.

Did this work before? N/A 

Does this work in other browsers? Yes

Chrome version: 58.0.3029.110  Channel: stable
OS Version: 
Flash Version: 

Chromium currently defines a LayoutTest which ostensibly covers this case [1],
but it does not seem to test the condition it documents. That apparent error
will be corrected when the test is migrated to the Web Platform Tests project
(see [2]), and this change produces a new test failure that will need to be
accounted for until Chromium's implementation can be made to match the relevant
specifications (i.e. Fetch and Service Workers) in this regard.

[1] https://chromium.googlesource.com/chromium/src.git/+/0f5b86386accbd17d06a26475df674a2e1df8bf2/third_party/WebKit/LayoutTests/http/tests/serviceworker/sync-xhr-doesnt-deadlock.html
[2] https://bugs.chromium.org/p/chromium/issues/detail?id=688116&desc=2