Import async-trait crate.

Bug: 164106399
Bug: 158290206
Test: mm
Change-Id: I0c4a491b785134e4ac1d5572e5ff94b8699dc0bc
diff --git a/tests/compiletest.rs b/tests/compiletest.rs
new file mode 100644
index 0000000..f9aea23
--- /dev/null
+++ b/tests/compiletest.rs
@@ -0,0 +1,6 @@
+#[rustversion::attr(not(nightly), ignore)]
+#[test]
+fn ui() {
+    let t = trybuild::TestCases::new();
+    t.compile_fail("tests/ui/*.rs");
+}