At the moment, when checking which messages should be sent to the client, we are checking if the window the message was emitted from belongs to the "target window tree" (see https://searchfox.org/mozilla-central/rev/1761c710b035d7dc8892dfa8e56589b4e095221f/devtools/server/actors/resources/error-messages.js#81-83 for example)

With Bug 1685500, we'll have targets for each document, so we can do an exact match on the window instead, as messages from iframes will be included from the iframes targets.

With dedicated targets for each window, we can now only check that the message
originates from the target window, and not from its window tree
Some tests that were assuming the iframe had the same target as the top level document
are updated.

Depends on D125833

https://hg.mozilla.org/mozilla-central/rev/7b38889adbb6