diff -r 000000000000 -r 6474c204b198 dom/ipc/PermissionMessageUtils.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/ipc/PermissionMessageUtils.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,68 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+#include "mozilla/dom/PermissionMessageUtils.h"
+#include "nsISerializable.h"
+#include "nsSerializationHelper.h"
+
+namespace IPC {
+
+void
+ParamTraits<Principal>::Write(Message* aMsg, const paramType& aParam) {
+  bool isNull = !aParam.mPrincipal;
+  WriteParam(aMsg, isNull);
+  if (isNull) {
+    return;
+  }
+
+  bool isSerialized = false;
+  nsCString principalString;
+  nsCOMPtr<nsISerializable> serializable = do_QueryInterface(aParam.mPrincipal);
+  if (serializable) {
+    nsresult rv = NS_SerializeToString(serializable, principalString);
+    if (NS_SUCCEEDED(rv)) {
+      isSerialized = true;
+    }
+  }
+
+  if (!isSerialized) {
+    NS_RUNTIMEABORT("Unable to serialize principal.");
+    return;
+  }
+
+  WriteParam(aMsg, principalString);
+}
+
+bool
+ParamTraits<Principal>::Read(const Message* aMsg, void** aIter, paramType* aResult)
+{
+  bool isNull;
+  if (!ReadParam(aMsg, aIter, &isNull)) {
+    return false;
+  }
+
+  if (isNull) {
+    aResult->mPrincipal = nullptr;
+    return true;
+  }
+
+  nsCString principalString;
+  if (!ReadParam(aMsg, aIter, &principalString)) {
+    return false;
+  }
+
+  nsCOMPtr<nsISupports> iSupports;
+  nsresult rv = NS_DeserializeObject(principalString, getter_AddRefs(iSupports));
+  NS_ENSURE_SUCCESS(rv, false);
+
+  nsCOMPtr<nsIPrincipal> principal = do_QueryInterface(iSupports);
+  NS_ENSURE_TRUE(principal, false);
+
+  principal.swap(aResult->mPrincipal);
+  return true;
+}
+
+} // namespace IPC
+