Implement new approach for debugging leaked wrapper object references (issue #2593)

libcef_dll/shutdown_checker.h

@@ -0,0 +1,19 @@
+// Copyright (c) 2019 The Chromium Embedded Framework 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 CEF_LIBCEF_DLL_SHUTDOWN_CHECKER_H_
+#define CEF_LIBCEF_DLL_SHUTDOWN_CHECKER_H_
+#pragma once
+
+namespace shutdown_checker {
+
+// Check that CEF objects are not held at CefShutdown.
+void AssertNotShutdown();
+
+// Called from libcef_dll.cc and libcef_dll_wrapper.cc.
+void SetIsShutdown();
+
+}  // namespace shutdown_checker
+
+#endif  // CEF_LIBCEF_DLL_SHUTDOWN_CHECKER_H_