DOMContentLoad for window.open

[diegocr]

Listening for DOMContentLoad and traversing through open tabs when disabling/updating to (un)patch window.open calls is overkill.

http-on-opening-request or just http-on-modify-request might be more suitable and it'll catch everything being loaded. However, it could slow down the browser considering we'll need to get the window associated with the channel every time a resource is being loaded... [Benchmarks time]