AU: Add support for persistent update engine preferences store.

SConstruct

 # Copyright (c) 2009 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.
 
 import os
 
 # Protobuffer compilation
 def ProtocolBufferEmitter(target, source, env):
   """ Inputs:
           target: list of targets to compile to
@@ skipping 196 matching lines @@
                    file_writer.cc
                    graph_utils.cc
                    gzip.cc
                    libcurl_http_fetcher.cc
                    marshal.glibmarshal.c
                    omaha_hash_calculator.cc
                    omaha_request_action.cc
                    omaha_request_params.cc
                    omaha_response_handler_action.cc
                    postinstall_runner_action.cc
+                   prefs.cc
                    set_bootable_flag_action.cc
                    simple_key_value_store.cc
                    split_file_writer.cc
                    subprocess.cc
                    tarjan.cc
                    topological_sort.cc
                    update_attempter.cc
                    update_metadata.pb.cc
                    utils.cc""")
 main = ['main.cc']
@@ skipping 13 matching lines @@
                             filesystem_copier_action_unittest.cc
                             filesystem_iterator_unittest.cc
                             graph_utils_unittest.cc
                             http_fetcher_unittest.cc
                             mock_http_fetcher.cc
                             omaha_hash_calculator_unittest.cc
                             omaha_request_action_unittest.cc
                             omaha_request_params_unittest.cc
                             omaha_response_handler_action_unittest.cc
                             postinstall_runner_action_unittest.cc
+                            prefs_unittest.cc
                             set_bootable_flag_action_unittest.cc
                             simple_key_value_store_unittest.cc
                             split_file_writer_unittest.cc
                             subprocess_unittest.cc
                             tarjan_unittest.cc
                             test_utils.cc
                             topological_sort_unittest.cc
                             utils_unittest.cc
                             zip_unittest.cc""")
 unittest_main = ['testrunner.cc']
@@ skipping 30 matching lines @@
                                   delta_generator_main)
 
 http_server_cmd = env.Program('test_http_server', 'test_http_server.cc')
 
 unittest_env = env.Clone()
 unittest_env.Append(LIBS=['gtest'])
 unittest_cmd = unittest_env.Program('update_engine_unittests',
                            unittest_sources + unittest_main)
 Clean(unittest_cmd, Glob('*.gcda') + Glob('*.gcno') + Glob('*.gcov') +
                     Split('html app.info'))