Add Drop impl for linked_list::DrainFilter

Author: tmccombs

src/liballoc/linked_list.rs

@@ -1071,6 +1071,15 @@ impl<'a, T, F> Iterator for DrainFilter<'a, T, F>
     }
 }
 
+#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
+impl<'a, T, F> Drop for DrainFilter<'a, T, F>
+    where F: FnMut(&mut T) -> bool,
+{
+    fn drop(&mut self) {
+        for _ in self { }
+    }
+}
+
 #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
 impl<'a, T: 'a + fmt::Debug, F> fmt::Debug for DrainFilter<'a, T, F>
     where F: FnMut(&mut T) -> bool