Import async-trait crate.

Bug: 164106399
Bug: 158290206
Test: mm
Change-Id: I0c4a491b785134e4ac1d5572e5ff94b8699dc0bc
diff --git a/tests/ui/missing-body.stderr b/tests/ui/missing-body.stderr
new file mode 100644
index 0000000..2d9b09c
--- /dev/null
+++ b/tests/ui/missing-body.stderr
@@ -0,0 +1,7 @@
+error: associated function in `impl` without body
+  --> $DIR/missing-body.rs:12:5
+   |
+12 |     async fn f(&self);
+   |     ^^^^^^^^^^^^^^^^^-
+   |                      |
+   |                      help: provide a definition for the function: `{ <body> }`