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diff --git a/js/xpconnect/wrappers/WrapperFactory.h b/js/xpconnect/wrappers/WrapperFactory.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef _xpc_WRAPPERFACTORY_H
+#define _xpc_WRAPPERFACTORY_H
+
+#include "js/Wrapper.h"
+
+namespace xpc {
+
+/**
+ * A wrapper that's only used for cross-origin objects. This should be
+ * just like a CrossCompartmentWrapper but (as an implementation
+ * detail) doesn't actually do any compartment-entering and (as an
+ * implementation detail) delegates all the security decisions and
+ * compartment-entering to the target object, which is always a
+ * proxy.
+ *
+ * We could also inherit from CrossCompartmentWrapper but then we
+ * would need to override all the proxy hooks to avoid the
+ * compartment-entering bits.
+ */
+class CrossOriginObjectWrapper : public js::Wrapper {
+ public:
+  // We want to claim to have a security policy, so code doesn't just
+  // CheckedUnwrap us willy-nilly.  But we're OK with the BaseProxyHandler
+  // implementation of enter(), which allows entering.  Our target is what
+  // really does the security checks.
+  //
+  // We don't want to inherit from CrossCompartmentWrapper, because we don't
+  // want the compartment-entering behavior it has.  But we do want to set the
+  // CROSS_COMPARTMENT flag on js::Wrapper so that we test true for
+  // is<js::CrossCompartmentWrapperObject> and so forth.
+  constexpr explicit CrossOriginObjectWrapper()
+      : js::Wrapper(CROSS_COMPARTMENT, /* aHasPrototype = */ false,
+                    /* aHasSecurityPolicy = */ true) {}
+
+  bool dynamicCheckedUnwrapAllowed(JS::Handle<JSObject*> obj,
+                                   JSContext* cx) const override;
+
+  // Cross origin objects should not participate in private fields.
+  virtual bool throwOnPrivateField() const override { return true; }
+
+  static const CrossOriginObjectWrapper singleton;
+};
+
+class WrapperFactory {
+ public:
+  enum {
+    WAIVE_XRAY_WRAPPER_FLAG = js::Wrapper::LAST_USED_FLAG << 1,
+    IS_XRAY_WRAPPER_FLAG = WAIVE_XRAY_WRAPPER_FLAG << 1
+  };
+
+  // Return true if any of any of the nested wrappers have the flag set.
+  static bool HasWrapperFlag(JSObject* wrapper, unsigned flag) {
+    unsigned flags = 0;
+    js::UncheckedUnwrap(wrapper, true, &flags);
+    return !!(flags & flag);
+  }
+
+  static bool IsXrayWrapper(JSObject* wrapper) {
+    return HasWrapperFlag(wrapper, IS_XRAY_WRAPPER_FLAG);
+  }
+
+  static bool IsCrossOriginWrapper(JSObject* obj) {
+    return (js::IsProxy(obj) &&
+            js::GetProxyHandler(obj) == &CrossOriginObjectWrapper::singleton);
+  }
+
+  static bool IsOpaqueWrapper(JSObject* obj);
+
+  static bool HasWaiveXrayFlag(JSObject* wrapper) {
+    return HasWrapperFlag(wrapper, WAIVE_XRAY_WRAPPER_FLAG);
+  }
+
+  static bool IsCOW(JSObject* wrapper);
+
+  static JSObject* GetXrayWaiver(JS::Handle<JSObject*> obj);
+  // If allowExisting is true, there is an existing waiver for obj in
+  // its scope, but we want to replace it with the new one.
+  static JSObject* CreateXrayWaiver(JSContext* cx, JS::Handle<JSObject*> obj,
+                                    bool allowExisting = false);
+  static JSObject* WaiveXray(JSContext* cx, JSObject* obj);
+
+  // Computes whether we should allow the creation of an Xray waiver from
+  // |target| to |origin|.
+  static bool AllowWaiver(JS::Compartment* target, JS::Compartment* origin);
+
+  // Convenience method for the above, operating on a wrapper.
+  static bool AllowWaiver(JSObject* wrapper);
+
+  // Prepare a given object for wrapping in a new compartment.
+  static void PrepareForWrapping(JSContext* cx, JS::Handle<JSObject*> scope,
+                                 JS::Handle<JSObject*> origObj,
+                                 JS::Handle<JSObject*> obj,
+                                 JS::Handle<JSObject*> objectPassedToWrap,
+                                 JS::MutableHandle<JSObject*> retObj);
+
+  // Rewrap an object that is about to cross compartment boundaries.
+  static JSObject* Rewrap(JSContext* cx, JS::Handle<JSObject*> existing,
+                          JS::Handle<JSObject*> obj);
+
+  // Wrap wrapped object into a waiver wrapper and then re-wrap it.
+  static bool WaiveXrayAndWrap(JSContext* cx, JS::MutableHandle<JS::Value> vp);
+  static bool WaiveXrayAndWrap(JSContext* cx,
+                               JS::MutableHandle<JSObject*> object);
+};
+
+}  // namespace xpc
+
+#endif /* _xpc_WRAPPERFACTORY_H */