Remove use of WS_EX_COMPOSITED for translucent windows.

ui/gfx/win/constants.h

+// Copyright 2017 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.
+
+#ifndef UI_GFX_WIN_CONSTANTS_H_
+#define UI_GFX_WIN_CONSTANTS_H_
+
+namespace gfx {
+
+// This property is put on an HWND so the compositor output knows to treat it
+// as transparent and draw to it using WS_EX_LAYERED (if using the software
+// compositor).
+const wchar_t kChromeWindowTranslucent[] = L"Chrome.WindowTranslucent";

[sky, 2017/04/20 17:26:28]

We also have ui/base/win/internal_constants.h. Can this move there? If it can't
for some reason, can you move the other one here? Also, should this be extern?

+
+}  // namespace gfx
+
+#endif  // UI_GFX_WIN_CONSTANTS_H_