A common handler for hanging_gets
Error returned if watch fails.
Handler for hanging gets. The common way to use this is to implement the Sender
trait for the FIDL responder that the handler is used for.
There should be one instance of HangingGetHandler per interface per connection, as the handler needs to keep track
of state per connection.
Trait that should be implemented to send data to the hanging get watcher.
Default change function that checks for equality