buffet: Remove DBusManager class

Move the TestMethod to the Manager, then remove the DBusManager
entirely.  This lets us turn the object at org/chromium/Buffet
into a pure object manager and removes a lot of boilerplate.

BUG=chromium:359190
TEST=buffet_client continues to demonstrate buffet functionality
through the TestMethod, which is now implementated by the Manager.

Change-Id: Ie9ecf0f7dd4dd50a3355ad7b06b8e2cfca71d9f9
Reviewed-on: https://chromium-review.googlesource.com/198760
Tested-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/buffet/dbus_constants.h b/buffet/dbus_constants.h
index 13c8a71..b7e9239 100644
--- a/buffet/dbus_constants.h
+++ b/buffet/dbus_constants.h
@@ -12,13 +12,9 @@
 // The service name claimed by the Buffet daemon.
 extern const char kServiceName[];
 
-// Interface implemented by the object at kRootServicePath.
-extern const char kRootInterface[];
+// The object at this path implements the ObjectManager interface.
 extern const char kRootServicePath[];
 
-// Methods exposed as part of kRootInterface.
-extern const char kRootTestMethod[];
-
 // Interface implemented by the object at kManagerServicePath.
 extern const char kManagerInterface[];
 extern const char kManagerServicePath[];
@@ -29,6 +25,7 @@
 extern const char kManagerStartRegisterDevice[];
 extern const char kManagerFinishRegisterDevice[];
 extern const char kManagerUpdateStateMethod[];
+extern const char kManagerTestMethod[];
 
 }  // namespace dbus_constants