Lower the I/O priority of the installer when resonable.

chrome/installer/setup/setup_main.cc

 // Copyright (c) 2012 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.
 
 #include <windows.h>
 #include <msi.h>
 #include <shellapi.h>
 #include <shlobj.h>
 
 #include <string>
@@ skipping 621 matching lines @@
     const InstallationState& original_state,
     const CommandLine& cmd_line,
     const MasterPreferences& prefs,
     const InstallerState& installer_state,
     installer::ArchiveType* archive_type,
     bool* delegated_to_existing) {
   DCHECK(archive_type);
   const bool system_install = installer_state.system_install();
   installer::InstallStatus install_status = installer::UNKNOWN_STATUS;
 
+  // Drop to background processing mode if the process was started below the
+  // normal process priority class.
+  VLOG_IF(1, installer::AdjustProcessPriority())

[cpu_(ooo_6.6-7.5), 2013/06/03 19:43:02]

I am always scared of calling actuall code inside logging macros. Eventually
somebody is going to create a configuration where this is a no op.

[grt (UTC plus 2), 2013/06/03 20:13:18]

Done.

+      << "Entered background processing mode.";
+
   // For install the default location for chrome.packed.7z is in current
   // folder, so get that value first.
   base::FilePath archive(cmd_line.GetProgram().DirName().Append(
       installer::kChromeCompressedArchive));
 
   // If --install-archive is given, get the user specified value
   if (cmd_line.HasSwitch(installer::switches::kInstallArchive)) {
     archive = cmd_line.GetSwitchValuePath(
         installer::switches::kInstallArchive);
   }
@@ skipping 1075 matching lines @@
   if (!(installer_state.is_msi() && is_uninstall))
     // Note that we allow the status installer::UNINSTALL_REQUIRES_REBOOT
     // to pass through, since this is only returned on uninstall which is
     // never invoked directly by Google Update.
     return_code = InstallUtil::GetInstallReturnCode(install_status);
 
   VLOG(1) << "Installation complete, returning: " << return_code;
 
   return return_code;
 }