AU: Speed up full update payload generation by running multiple threads.

SConstruct

 # 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.
 
 import os
 
 # Protobuffer compilation
 def ProtocolBufferEmitter(target, source, env):
   """ Inputs:
           target: list of targets to compile to
@@ skipping 231 matching lines @@
                    delta_diff_generator.cc
                    delta_performer.cc
                    download_action.cc
                    extent_mapper.cc
                    extent_ranges.cc
                    extent_writer.cc
                    filesystem_copier_action.cc
                    filesystem_iterator.cc
                    file_writer.cc
                    flimflam_proxy.cc
+                   full_update_generator.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
                    payload_signer.cc
                    postinstall_runner_action.cc
@@ skipping 21 matching lines @@
                             delta_diff_generator_unittest.cc
                             delta_performer_unittest.cc
                             download_action_unittest.cc
                             extent_mapper_unittest.cc
                             extent_ranges_unittest.cc
                             extent_writer_unittest.cc
                             file_writer_unittest.cc
                             filesystem_copier_action_unittest.cc
                             filesystem_iterator_unittest.cc
                             flimflam_proxy_unittest.cc
+                            full_update_generator_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
                             payload_signer_unittest.cc
                             postinstall_runner_action_unittest.cc
                             prefs_unittest.cc
@@ skipping 44 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=['gmock', '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'))