diff -r 000000000000 -r 6474c204b198 ipc/glue/FileDescriptorUtils.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ipc/glue/FileDescriptorUtils.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,78 @@
+/* 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 "FileDescriptorUtils.h"
+
+#include "nsIEventTarget.h"
+
+#include "nsCOMPtr.h"
+#include "nsDebug.h"
+#include "nsNetCID.h"
+#include "nsServiceManagerUtils.h"
+#include "nsThreadUtils.h"
+#include "prio.h"
+#include "private/pprio.h"
+
+using mozilla::ipc::CloseFileRunnable;
+
+#ifdef DEBUG
+
+CloseFileRunnable::CloseFileRunnable(const FileDescriptor& aFileDescriptor)
+: mFileDescriptor(aFileDescriptor)
+{
+  MOZ_ASSERT(aFileDescriptor.IsValid());
+}
+
+#endif // DEBUG
+
+CloseFileRunnable::~CloseFileRunnable()
+{
+  if (mFileDescriptor.IsValid()) {
+    // It's probably safer to take the main thread IO hit here rather than leak
+    // the file descriptor.
+    CloseFile();
+  }
+}
+
+NS_IMPL_ISUPPORTS(CloseFileRunnable, nsIRunnable)
+
+void
+CloseFileRunnable::Dispatch()
+{
+  nsCOMPtr<nsIEventTarget> eventTarget =
+    do_GetService(NS_STREAMTRANSPORTSERVICE_CONTRACTID);
+  NS_ENSURE_TRUE_VOID(eventTarget);
+
+  nsresult rv = eventTarget->Dispatch(this, NS_DISPATCH_NORMAL);
+  NS_ENSURE_SUCCESS_VOID(rv);
+}
+
+void
+CloseFileRunnable::CloseFile()
+{
+  // It's possible for this to happen on the main thread if the dispatch to the
+  // stream service fails so we can't assert the thread on which we're running.
+
+  MOZ_ASSERT(mFileDescriptor.IsValid());
+
+  PRFileDesc* fd =
+    PR_ImportFile(PROsfd(mFileDescriptor.PlatformHandle()));
+  NS_WARN_IF_FALSE(fd, "Failed to import file handle!");
+
+  mFileDescriptor = FileDescriptor();
+
+  if (fd) {
+    PR_Close(fd);
+    fd = nullptr;
+  }
+}
+
+NS_IMETHODIMP
+CloseFileRunnable::Run()
+{
+  MOZ_ASSERT(!NS_IsMainThread());
+
+  CloseFile();
+  return NS_OK;
+}