buffet: Switch buffet::Manager to use DBusObject

Use DBusObject to implement "/org/chromium/Buffet/Manager" object.

BUG=chromium:374864
TEST=USE=buffet P2_TEST_FILTER="buffet::*" FEATURES=test emerge-link platform2

Change-Id: I91141ce76a1dbd4478577f2f7548f99a33241fb5
Reviewed-on: https://chromium-review.googlesource.com/212682
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/buffet/device_registration_info.h b/buffet/device_registration_info.h
index df23e36..1985bb6 100644
--- a/buffet/device_registration_info.h
+++ b/buffet/device_registration_info.h
@@ -96,7 +96,7 @@
   // and so on. If a particular key-value pair is omitted, a default value
   // is used when possible. Returns a device claim ID on success.
   std::string StartRegistration(
-    const std::map<std::string, std::shared_ptr<base::Value>>& params,
+    const std::map<std::string, std::unique_ptr<base::Value>>& params,
     chromeos::ErrorPtr* error);
 
   // Finalizes the device registration. If |user_auth_code| is provided, then