Adding rtc::Unretained to allow avoiding rtc::Bind reference capture.

In some rare circumstances, capturing a reference may be undesired. For
example, when creating an asynchronous task owned by the object itself,
the object may not need or want this task to keep itself alive.

BUG=None

Review-Url: https://codereview.webrtc.org/2711113008
Cr-Commit-Position: refs/heads/master@{#16840}
diff --git a/webrtc/base/bind_unittest.cc b/webrtc/base/bind_unittest.cc
index 3331591..c97a555 100644
--- a/webrtc/base/bind_unittest.cc
+++ b/webrtc/base/bind_unittest.cc
@@ -87,6 +87,8 @@
 EXPECT_IS_CAPTURED_AS_PTR(A);
 EXPECT_IS_CAPTURED_AS_PTR(D);
 EXPECT_IS_CAPTURED_AS_PTR(RefCountInterface*);
+EXPECT_IS_CAPTURED_AS_PTR(
+    decltype(Unretained<RefCountedObject<RefCountInterface>>));
 
 EXPECT_IS_CAPTURED_AS_SCOPED_REFPTR(RefCountInterface);
 EXPECT_IS_CAPTURED_AS_SCOPED_REFPTR(B);