style: Add refcount logging to servo_arc.

Differential Revision: https://phabricator.services.mozilla.com/D32173

components/style/shared_lock.rs

@@ -71,6 +71,14 @@ impl SharedRwLock {
         }
     }
 
+    /// Create a new global shared lock (gecko).
+    #[cfg(feature = "gecko")]
+    pub fn new_leaked() -> Self {
+        SharedRwLock {
+            cell: Some(Arc::new_leaked(AtomicRefCell::new(SomethingZeroSizedButTyped))),
+        }
+    }
+
     /// Create a new read-only shared lock (gecko).
     #[cfg(feature = "gecko")]
     pub fn read_only() -> Self {