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

chrome/installer/setup/setup_util.h

 // 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.
 //
 // This file declares util functions for setup project.
 
 #ifndef CHROME_INSTALLER_SETUP_SETUP_UTIL_H_
 #define CHROME_INSTALLER_SETUP_SETUP_UTIL_H_
 
 #include <windows.h>
@@ skipping 63 matching lines @@
 // Returns true if the product |type| will be installed after the current
 // setup.exe instance have carried out installation / uninstallation, at
 // the level specified by |installer_state|.
 // This function only returns meaningful results for install and update
 // operations if called after CheckPreInstallConditions (see setup_main.cc).
 bool WillProductBePresentAfterSetup(
     const installer::InstallerState& installer_state,
     const installer::InstallationState& machine_state,
     BrowserDistribution::Type type);
 
+// Drops the process down to background processing mode on supported OSes if it
+// was launched below the normal process priority. Returns true when background
+// procesing mode is entered.
+bool AdjustProcessPriority();
+
 // This class will enable the privilege defined by |privilege_name| on the
 // current process' token. The privilege will be disabled upon the
 // ScopedTokenPrivilege's destruction (unless it was already enabled when the
 // ScopedTokenPrivilege object was constructed).
 // Some privileges might require admin rights to be enabled (check is_enabled()
 // to know whether |privilege_name| was successfully enabled).
 class ScopedTokenPrivilege {
  public:
   explicit ScopedTokenPrivilege(const wchar_t* privilege_name);
   ~ScopedTokenPrivilege();
@@ skipping 12 matching lines @@
   // The previous state of the privilege this object is responsible for. As set
   // by AdjustTokenPrivileges() upon construction.
   TOKEN_PRIVILEGES previous_privileges_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(ScopedTokenPrivilege);
 };
 
 }  // namespace installer
 
 #endif  // CHROME_INSTALLER_SETUP_SETUP_UTIL_H_