`externally_connectable.matches` with `runtime.sendMessage` fails

Currently calling runtime.sendMessage from a MAIN world script fails with externally_connectable.matches.

This prevents some chrome extensions to work which rely on this functionality.

Keep in mind this feature is currently only supported in Chrome and Safari. Not yet in Firefox. This is tracked at:
https://bugzilla.mozilla.org/show_bug.cgi?id=1319168

Version 1.0.6 (145), WebKit 624.1.7

Tahoe (26)

@dino @nrudnyk amazing, thanks!