Revert "remove arbiter TLS item storage"

This reverts commit 3e6f69885c.

actix-rt/tests/tests.rs

@@ -140,6 +140,35 @@ fn arbiter_drop_no_panic_fut() {
     arbiter.join().unwrap();
 }
 
+#[test]
+fn arbiter_item_storage() {
+    let _ = System::new();
+
+    let arbiter = Arbiter::new();
+
+    assert!(!Arbiter::contains_item::<u32>());
+    Arbiter::set_item(42u32);
+    assert!(Arbiter::contains_item::<u32>());
+
+    Arbiter::get_item(|&item: &u32| assert_eq!(item, 42));
+    Arbiter::get_mut_item(|&mut item: &mut u32| assert_eq!(item, 42));
+
+    let thread = thread::spawn(move || {
+        Arbiter::get_item(|&_item: &u32| unreachable!("u32 not in this thread"));
+    })
+    .join();
+    assert!(thread.is_err());
+
+    let thread = thread::spawn(move || {
+        Arbiter::get_mut_item(|&mut _item: &mut i8| unreachable!("i8 not in this thread"));
+    })
+    .join();
+    assert!(thread.is_err());
+
+    arbiter.stop();
+    arbiter.join().unwrap();
+}
+
 #[test]
 #[should_panic]
 fn no_system_current_panic() {