Monkey patch Broadcast Channel to send messages to current context

|---same javascript context----------|
| |-patched test_channel source----| |
| | Send messages here!            | |
| |--------------------------------| |
|                                    |
| |-test_channel-------------------| |
| | Recieve messages here          | |
| |--------------------------------| |
|                                    |
| |-test_channel-------------------| |
| | and here!                      | |
| |--------------------------------| |
|------------------------------------|