user_manager component: Add UserManagerBase class.

components/session_manager.gypi

 # Copyright 2014 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.
 
 {
   'targets': [
     {
       'target_name': 'session_manager_component',
       'type': '<(component)',
       'dependencies': [
         '../base/base.gyp:base',
       ],
       'include_dirs': [
         '..',
       ],
       'defines': [
         'SESSION_IMPLEMENTATION',
       ],
       'sources': [
         'session_manager/core/session_manager.h',
         'session_manager/core/session_manager.cc',
         'session_manager/session_manager_export.h',
       ],
+      'conditions': [
+        ['chromeos == 1', {
+          'dependencies': [
+            '<(DEPTH)/chromeos/chromeos.gyp:chromeos',
+          ],
+        }],
+      ],
     },
   ],
 }