New default IClientCallback implementation

Add a default IClientCallback implementation which exits once all
watched services have no more clients. This is useful for lazy HALs.

Test: Use DefaultCounterExitCallback to register a HAL that implements
      two interfaces and check that it exits when both interfaces are
      unused.
Change-Id: Ifcc53631e284375a436d618e84e9546a5e53844a
diff --git a/transport/Android.bp b/transport/Android.bp
index f783022..6518177 100644
--- a/transport/Android.bp
+++ b/transport/Android.bp
@@ -65,6 +65,7 @@
 
     srcs: [
         "HidlBinderSupport.cpp",
+        "HidlLazyUtils.cpp",
         "HidlPassthroughSupport.cpp",
         "HidlTransportSupport.cpp",
         "HidlTransportUtils.cpp",