Add debug::Alias for version to track unexpected DwmIsCompositionEnabled call

ui/base/win/shell.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 "ui/base/win/shell.h"
 
 #include <dwmapi.h>
 #include <shlobj.h>  // Must be before propkey.
 #include <propkey.h>
 #include <shellapi.h>
 
 #include "base/command_line.h"
+#include "base/debug/alias.h"
 #include "base/files/file_path.h"
 #include "base/native_library.h"
 #include "base/strings/string_util.h"
 #include "base/win/metro.h"
 #include "base/win/scoped_comptr.h"
 #include "base/win/win_util.h"
 #include "base/win/windows_version.h"
 #include "ui/base/ui_base_switches.h"
 
 namespace ui {
@@ skipping 116 matching lines @@
 
 bool IsAeroGlassEnabled() {
   // For testing in Win8 (where it is not possible to disable composition) the
   // user can specify this command line switch to mimic the behavior.  In this
   // mode, cross-HWND transparency is not supported and various types of
   // widgets fallback to more simplified rendering behavior.
   if (CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kDisableDwmComposition))
     return false;
 
-  if (base::win::GetVersion() < base::win::VERSION_VISTA)
+  base::win::Version version = base::win::GetVersion();
+  base::debug::Alias(&version);  // TODO(scottmg): http://crbug.com/431549.
+  if (version < base::win::VERSION_VISTA)
     return false;
   // If composition is not enabled, we behave like on XP.
   BOOL enabled = FALSE;
   return SUCCEEDED(DwmIsCompositionEnabled(&enabled)) && enabled;
 }
 
 }  // namespace win
 }  // namespace ui