Wrap IntoFuture around Cancellable::future

Implement IntoFuture for Cancellable as a dead-simple wrapper around the
existing Cancellable::future.

See #1512

Author: swsnr

gio/src/cancellable.rs

@@ -1,6 +1,6 @@
 // Take a look at the license at the top of the repository in the LICENSE file.
 
-use std::num::NonZeroU64;
+use std::{future::IntoFuture, num::NonZeroU64};
 
 use futures_channel::oneshot;
 use futures_core::Future;
@@ -146,6 +146,16 @@ pub trait CancellableExtManual: IsA<Cancellable> {
 
 impl<O: IsA<Cancellable>> CancellableExtManual for O {}
 
+impl IntoFuture for Cancellable {
+    type Output = ();
+
+    type IntoFuture = std::pin::Pin<Box<dyn Future<Output = ()> + Send + Sync + 'static>>;
+
+    fn into_future(self) -> Self::IntoFuture {
+        self.future()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;