Remove use of WS_EX_COMPOSITED for translucent windows.

ui/base/win/internal_constants.h

Index: ui/base/win/internal_constants.h
diff --git a/ui/base/win/internal_constants.h b/ui/base/win/internal_constants.h
index d81c34de4f10aec1d914442c79ec2cecaff43dad..65f025f397ab1bb2bdd55f6702ce10929b96297f 100644
--- a/ui/base/win/internal_constants.h
+++ b/ui/base/win/internal_constants.h
@@ -13,6 +13,11 @@ namespace ui {
 // touch based WM_MOUSEACTIVATE message.
 UI_BASE_EXPORT extern const wchar_t kIgnoreTouchMouseActivateForWindow[];
 
+// 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).
+UI_BASE_EXPORT extern const wchar_t kWindowTranslucent[];
+
 }  // namespace ui
 
 #endif  // UI_BASE_WIN_INTERNAL_CONSTANTS_H_