Make getHwAvSync strongly typed above libaudiohal

This CL lays the foundation and pattern for converting more parameters
to a strongly typed interface.

Test: TBD
Change-Id: I5503da3f68c543e441ede4d381518a8e5601fe8c
diff --git a/media/libaudiohal/impl/DeviceHalHidl.h b/media/libaudiohal/impl/DeviceHalHidl.h
index cd9535e..8a97a55 100644
--- a/media/libaudiohal/impl/DeviceHalHidl.h
+++ b/media/libaudiohal/impl/DeviceHalHidl.h
@@ -134,6 +134,8 @@
 
     status_t setConnectedState(const struct audio_port_v7 *port, bool connected) override;
 
+    error::Result<audio_hw_sync_t> getHwAvSync() override;
+
     status_t dump(int fd, const Vector<String16>& args) override;
 
   private: