buffet: libchromeos: Migrate ExportedPropertySet to libchromeos

We want to reuse this in peerd.  As a side effect, we're forced to
pull parts of dbus_utils, and patch up a bunch of namespace issues.

BUG=chromium:398626
TEST=libchromeos/buffet unittests.

Change-Id: Id7f40c95d1677ec0460ce1677c0933478a315d8c
Reviewed-on: https://chromium-review.googlesource.com/211483
Tested-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Christopher Wiley <wiley@chromium.org>
diff --git a/buffet/dbus_utils.cc b/buffet/dbus_utils.cc
index 5c02fb3..099abc1 100644
--- a/buffet/dbus_utils.cc
+++ b/buffet/dbus_utils.cc
@@ -4,6 +4,8 @@
 
 #include "buffet/dbus_utils.h"
 
+#include <string>
+
 #include <base/bind.h>
 #include <base/logging.h>
 
@@ -29,14 +31,6 @@
 
 }  // namespace
 
-scoped_ptr<dbus::Response> GetBadArgsError(dbus::MethodCall* method_call,
-                                           const std::string& message) {
-  LOG(ERROR) << "Error while handling DBus call: " << message;
-  scoped_ptr<dbus::ErrorResponse> resp(dbus::ErrorResponse::FromMethodCall(
-      method_call, "org.freedesktop.DBus.Error.InvalidArgs", message));
-  return scoped_ptr<dbus::Response>(resp.release());
-}
-
 scoped_ptr<dbus::Response> GetDBusError(dbus::MethodCall* method_call,
                                         const Error* error) {
   std::string message;