Create a PrefStore in support of Blimp metrics collection.

components/prefs/prefs.gyp

 # Copyright (c) 2013 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': 'prefs',
       'type': '<(component)',
       'dependencies': [
         '../../base/base.gyp:base',
       ],
       'include_dirs': [
         '../..',
       ],
       'defines': [
         'COMPONENTS_PREFS_IMPLEMENTATION',
       ],
       'sources': [
         'default_pref_store.cc',
         'default_pref_store.h',
+        'in_memory_pref_store.cc',
+        'in_memory_pref_store.h',
         'json_pref_store.cc',
         'json_pref_store.h',
         'overlay_user_pref_store.cc',
         'overlay_user_pref_store.h',
         'pref_change_registrar.cc',
         'pref_change_registrar.h',
         'pref_member.cc',
         'pref_member.h',
         'pref_notifier_impl.cc',
         'pref_notifier_impl.h',
@@ skipping 46 matching lines @@
         'pref_store_observer_mock.cc',
         'pref_store_observer_mock.h',
         'testing_pref_service.cc',
         'testing_pref_service.h',
         'testing_pref_store.cc',
         'testing_pref_store.h',
       ],
     },
   ],
 }