Auto merge of #15368 - szeged:get_availability, r=nox

Implement GetAvailability for Bluetooth

<!-- Please describe your changes on the following line: -->
This implements the [getAvailability](https://webbluetoothcg.github.io/web-bluetooth/#dom-bluetooth-getavailability) function from the spec.

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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- [X] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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components/script/dom/bluetooth.rs

@@ -443,6 +443,18 @@ impl BluetoothMethods for Bluetooth {
         return p;
     }
 
+    #[allow(unrooted_must_root)]
+    // https://webbluetoothcg.github.io/web-bluetooth/#dom-bluetooth-getavailability
+    fn GetAvailability(&self) -> Rc<Promise> {
+        let p = Promise::new(&self.global());
+        // Step 1. We did not override the method
+        // Step 2 - 3. in handle_response
+        let sender = response_async(&p, self);
+        self.get_bluetooth_thread().send(
+            BluetoothRequest::GetAvailability(sender)).unwrap();
+        p
+    }
+
     // https://webbluetoothcg.github.io/web-bluetooth/#dom-bluetooth-onavailabilitychanged
     event_handler!(availabilitychanged, GetOnavailabilitychanged, SetOnavailabilitychanged);
 }
@@ -466,6 +478,11 @@ impl AsyncBluetoothListener for Bluetooth {
                 // Step 5.
                 promise.resolve_native(promise_cx, &bt_device);
             },
+            // https://webbluetoothcg.github.io/web-bluetooth/#dom-bluetooth-getavailability
+            // Step 2 - 3.
+            BluetoothResponse::GetAvailability(is_available) => {
+                promise.resolve_native(promise_cx, &is_available);
+            }
             _ => promise.reject_error(promise_cx, Error::Type("Something went wrong...".to_owned())),
         }
     }

components/script/dom/webidls/Bluetooth.webidl

@@ -29,8 +29,8 @@ dictionary RequestDeviceOptions {
 
 [Pref="dom.bluetooth.enabled"]
 interface Bluetooth : EventTarget {
-  // [SecureContext]
-  // Promise<boolean> getAvailability();
+  [SecureContext]
+  Promise<boolean> getAvailability();
   [SecureContext]
   attribute EventHandler onavailabilitychanged;
   // [SecureContext, SameObject]