Errors while deleting old version dirs no longer cause them to grow in odd ways.

chrome/installer/setup/install_worker.cc

 // Copyright (c) 2011 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 contains the definitions of the installer functions that build
 // the WorkItemList used to install the application.
 
 #include "chrome/installer/setup/install_worker.h"
 
 #include <shlobj.h>
@@ skipping 736 matching lines @@
                              WorkItem::ALWAYS_MOVE);
 
   // Copy the default Dictionaries only if the folder doesn't exist already.
   // TODO(grt): Use AddMoveTreeWorkItem in a conditional WorkItemList, which
   // will be more efficient in space and time.
   install_list->AddCopyTreeWorkItem(
       src_path.Append(installer::kDictionaries).value(),
       target_path.Append(installer::kDictionaries).value(),
       temp_path.value(), WorkItem::IF_NOT_PRESENT);
 
-  // Delete any old_chrome.exe if present.
+  // Delete any old_chrome.exe if present (ignore failure if it's in use).
   install_list->AddDeleteTreeWorkItem(
-      target_path.Append(installer::kChromeOldExe), temp_path);
+      target_path.Append(installer::kChromeOldExe), temp_path)
+      ->set_ignore_failure(true);
 
   // Copy installer in install directory and
   // add shortcut in Control Panel->Add/Remove Programs.
   AddInstallerCopyTasks(installer_state, setup_path, archive_path, temp_path,
                         new_version, install_list);
 
   const HKEY root = installer_state.root_key();
 
   const Products& products = installer_state.products();
   for (size_t i = 0; i < products.size(); ++i) {
@@ skipping 449 matching lines @@
     } else {
       DCHECK(operation == REMOVE_COMMAND);
       work_item_list->AddDeleteRegKeyWorkItem(installer_state.root_key(),
                                               cmd_key)->set_log_message(
           "removing quick-enable-cf command");
     }
   }
 }
 
 }  // namespace installer