Add a scoping object to help block scripting during plugin destruction.

public/web/WebReentrantScriptForbiddenScope.h

Index: public/web/WebReentrantScriptForbiddenScope.h
diff --git a/public/web/WebReentrantScriptForbiddenScope.h b/public/web/WebReentrantScriptForbiddenScope.h
new file mode 100644
index 0000000000000000000000000000000000000000..b5086a659887799955608baa35cd7d6f634f3320
--- /dev/null
+++ b/public/web/WebReentrantScriptForbiddenScope.h
@@ -0,0 +1,20 @@
+// Copyright 2015 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 WebReentrantScriptForbiddenScope_h
+#define WebReentrantScriptForbiddenScope_h
+
+#include "public/platform/WebCommon.h"
+
+namespace blink {
+
+class BLINK_EXPORT WebReentrantScriptForbiddenScope {
+public:
+    WebReentrantScriptForbiddenScope() = delete;
+    static bool isForbidden();
+};
+
+} // namespace blink
+
+#endif // WebReentrantScriptForbiddenScope_h