Update the remaining include paths of base/string_piece.h to its new location.

dbus/object_proxy.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef DBUS_OBJECT_PROXY_H_
 #define DBUS_OBJECT_PROXY_H_
 
 #include <dbus/dbus.h>
 
 #include <map>
 #include <set>
 #include <string>
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
-#include "base/string_piece.h"
+#include "base/strings/string_piece.h"
 #include "base/time.h"
 #include "dbus/dbus_export.h"
 #include "dbus/object_path.h"
 
 namespace dbus {
 
 class Bus;
 class ErrorResponse;
 class MethodCall;
 class Response;
@@ skipping 254 matching lines @@
 
   // Known name owner of the well-known bus name represnted by |service_name_|.
   std::string service_name_owner_;
 
   DISALLOW_COPY_AND_ASSIGN(ObjectProxy);
 };
 
 }  // namespace dbus
 
 #endif  // DBUS_OBJECT_PROXY_H_