There seems to be a compatibility issue when reloading iframe controlled by a service worker after unregistering or re-registering. 

We have to check whether "Clear" and "Activate"
process should be invoked after reloading the only controlled iframe or not, and add tests for confirmation.

Discussion in the expected behavior was around here: http://crrev.com/1865103003#msg29

Landed/ongoing patches
- https://codereview.chromium.org/1865103003/
- https://codereview.chromium.org/1886953003/