ProcessSingleton now uses base::win::MessageWindow to create a message-only window.

chrome/common/chrome_constants.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.
 
 // A handful of resource-like constants related to the Chrome application.
 
 #ifndef CHROME_COMMON_CHROME_CONSTANTS_H_
 #define CHROME_COMMON_CHROME_CONSTANTS_H_
 
 #include "base/files/file_path.h"
@@ skipping 22 matching lines @@
 // named Chromium Helper.app, helper executables could show up at any of
 // Chromium Helper.app/Contents/MacOS/Chromium Helper,
 // Chromium Helper EN.app/Contents/MacOS/Chromium Helper EN, and
 // Chromium Helper MF.app/Contents/MacOS/Chromium Helper MF.
 extern const base::FilePath::CharType* const kHelperFlavorSuffixes[];
 #endif  // OS_MACOSX
 #if defined(OS_WIN)
 extern const base::FilePath::CharType kMetroDriverDll[];
 extern const wchar_t kStatusTrayWindowClass[];
 #endif  // defined(OS_WIN)
-extern const wchar_t kMessageWindowClass[];
 extern const wchar_t kCrashReportLog[];
 extern const wchar_t kTestingInterfaceDLL[];
 extern const char    kInitialProfile[];
 extern const char    kMultiProfileDirPrefix[];
 extern const wchar_t kBrowserResourcesDll[];
 extern const base::FilePath::CharType kExtensionFileExtension[];
 extern const base::FilePath::CharType kExtensionKeyFileExtension[];
 
 // filenames
 #if defined(OS_ANDROID)
@@ skipping 84 matching lines @@
 #if defined(OS_CHROMEOS)
 // Chrome OS profile directories have custom prefix.
 // Profile path format: [user_data_dir]/u-[$hash]
 // Ex.: /home/chronos/u-0123456789
 extern const char kProfileDirPrefix[];
 #endif
 
 }  // namespace chrome
 
 #endif  // CHROME_COMMON_CHROME_CONSTANTS_H_