update_engine_client: Clarify error message.

update_engine_client.cc

 // Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <string>
 
 #include <gflags/gflags.h>
 #include <glib.h>
 
 #include "update_engine/marshal.glibmarshal.h"
@@ skipping 31 matching lines @@
   bus = dbus_g_bus_get(DBUS_BUS_SYSTEM, &error);
   if (!bus) {
     LOG(FATAL) << "Failed to get bus";
   }
   proxy = dbus_g_proxy_new_for_name_owner(bus,
                                           kUpdateEngineServiceName,
                                           kUpdateEngineServicePath,
                                           kUpdateEngineServiceInterface,
                                           &error);
   if (!proxy) {
-    LOG(FATAL) << "Error getting proxy: " << GetGErrorMessage(error);
+    LOG(FATAL) << "Error getting dbus proxy for "
+               << kUpdateEngineServiceName << ": " << GetGErrorMessage(error);
   }
   *out_proxy = proxy;
   return true;
 }
 
 static void StatusUpdateSignalHandler(DBusGProxy* proxy,
                                       int64_t last_checked_time,
                                       double progress,
                                       gchar* current_operation,
                                       gchar* new_version,
@@ skipping 188 matching lines @@
 
   if (FLAGS_reboot) {
     LOG(INFO) << "Requesting a reboot...";
     CHECK(RebootIfNeeded());
     return 0;
   }
 
   LOG(INFO) << "No flags specified. Exiting.";
   return 0;
 }