Use IBinder to uniquely identify binder callbacks.

The callback pointer might be different for the same callback, convert
it to IBinder and use that to identify callbacks instead.

Bug: 62293007
Test: mma

Change-Id: Ibd1c2de1192dd7d4f4bc498b0590f5b7f3de3aff
diff --git a/binder_service_android.h b/binder_service_android.h
index 375dad4..7d66fcc 100644
--- a/binder_service_android.h
+++ b/binder_service_android.h
@@ -73,7 +73,7 @@
   // Remove the passed |callback| from the list of registered callbacks. Called
   // on unbind() or whenever the callback object is destroyed.
   // Returns true on success.
-  bool UnbindCallback(android::os::IUpdateEngineCallback* callback);
+  bool UnbindCallback(const IBinder* callback);
 
   // List of currently bound callbacks.
   std::vector<android::sp<android::os::IUpdateEngineCallback>> callbacks_;