add tests to a few edge cases in method lookup

These aren't fixed by this PR, but were broken in a few older attempts
at it. Make sure they don't regress.

src/test/ui/methods/method-trait-object-with-hrtb.rs

@@ -0,0 +1,41 @@
+// compile-pass
+
+// Check that method probing ObjectCandidate works in the presence of
+// auto traits and/or HRTBs.
+
+mod internal {
+    pub trait MyObject<'a> {
+        type Output;
+
+        fn foo(&self) -> Self::Output;
+    }
+
+    impl<'a> MyObject<'a> for () {
+        type Output = &'a u32;
+
+        fn foo(&self) -> Self::Output { &4 }
+    }
+}
+
+fn t1(d: &dyn for<'a> internal::MyObject<'a, Output=&'a u32>) {
+    d.foo();
+}
+
+fn t2(d: &dyn internal::MyObject<'static, Output=&'static u32>) {
+    d.foo();
+}
+
+fn t3(d: &(dyn for<'a> internal::MyObject<'a, Output=&'a u32> + Sync)) {
+    d.foo();
+}
+
+fn t4(d: &(dyn internal::MyObject<'static, Output=&'static u32> + Sync)) {
+    d.foo();
+}
+
+fn main() {
+    t1(&());
+    t2(&());
+    t3(&());
+    t4(&());
+}