AU: Speed up updates by using buffered writes.

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 175 matching lines @@
 
 env.DbusBindings('update_engine.dbusclient.h', 'update_engine.xml')
 
 env.GlibMarshal('marshal.glibmarshal.c', 'marshal.list')
 
 if ARGUMENTS.get('debug', 0):
   env['CCFLAGS'] += ' -fprofile-arcs -ftest-coverage'
   env['LIBS'] += ['bz2', 'gcov']
 
 sources = Split("""action_processor.cc
+                   buffered_file_writer.cc
                    bzip.cc
                    bzip_extent_writer.cc
                    cycle_breaker.cc
                    dbus_service.cc
                    decompressing_file_writer.cc
                    delta_diff_generator.cc
                    delta_performer.cc
                    download_action.cc
                    extent_mapper.cc
                    extent_writer.cc
@@ skipping 19 matching lines @@
                    topological_sort.cc
                    update_attempter.cc
                    update_check_scheduler.cc
                    update_metadata.pb.cc
                    utils.cc""")
 main = ['main.cc']
 
 unittest_sources = Split("""action_unittest.cc
                             action_pipe_unittest.cc
                             action_processor_unittest.cc
+                            buffered_file_writer_unittest.cc
                             bzip_extent_writer_unittest.cc
                             cycle_breaker_unittest.cc
                             decompressing_file_writer_unittest.cc
                             delta_diff_generator_unittest.cc
                             delta_performer_unittest.cc
                             download_action_unittest.cc
                             extent_mapper_unittest.cc
                             extent_writer_unittest.cc
                             file_writer_unittest.cc
                             filesystem_copier_action_unittest.cc
@@ skipping 53 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'))