diff -r 000000000000 -r 6474c204b198 dom/file/MetadataHelper.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/file/MetadataHelper.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,96 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=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/. */
+
+#include "MetadataHelper.h"
+
+#include "LockedFile.h"
+
+USING_FILE_NAMESPACE
+
+nsresult
+MetadataHelper::DoAsyncRun(nsISupports* aStream)
+{
+  bool readWrite = mLockedFile->mMode == FileMode::Readwrite;
+
+  nsRefPtr<AsyncMetadataGetter> getter =
+    new AsyncMetadataGetter(aStream, mParams, readWrite);
+
+  nsresult rv = getter->AsyncWork(this, nullptr);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return NS_OK;
+}
+
+nsresult
+MetadataHelper::GetSuccessResult(JSContext* aCx,
+                                 JS::MutableHandle<JS::Value> aVal)
+{
+  JS::Rooted<JSObject*> obj(aCx, JS_NewObject(aCx, nullptr, JS::NullPtr(),
+                                              JS::NullPtr()));
+  NS_ENSURE_TRUE(obj, NS_ERROR_OUT_OF_MEMORY);
+
+  if (mParams->SizeRequested()) {
+    JS::Rooted<JS::Value> val(aCx, JS_NumberValue(mParams->Size()));
+
+    if (!JS_DefineProperty(aCx, obj, "size", val, JSPROP_ENUMERATE)) {
+      return NS_ERROR_FAILURE;
+    }
+  }
+
+  if (mParams->LastModifiedRequested()) {
+    double msec = mParams->LastModified();
+    JSObject *date = JS_NewDateObjectMsec(aCx, msec);
+    NS_ENSURE_TRUE(date, NS_ERROR_OUT_OF_MEMORY);
+
+    JS::Rooted<JS::Value> dateRoot(aCx, JS::ObjectValue(*date));
+    if (!JS_DefineProperty(aCx, obj, "lastModified", dateRoot,
+                           JSPROP_ENUMERATE)) {
+      return NS_ERROR_FAILURE;
+    }
+  }
+
+  aVal.setObject(*obj);
+  return NS_OK;
+}
+
+nsresult
+MetadataHelper::AsyncMetadataGetter::DoStreamWork(nsISupports* aStream)
+{
+  nsresult rv;
+
+  if (mReadWrite) {
+    // Force a flush (so all pending writes are flushed to the disk and file
+    // metadata is updated too).
+
+    nsCOMPtr<nsIOutputStream> ostream = do_QueryInterface(aStream);
+    NS_ASSERTION(ostream, "This should always succeed!");
+
+    rv = ostream->Flush();
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  nsCOMPtr<nsIFileMetadata> metadata = do_QueryInterface(aStream);
+
+  if (mParams->SizeRequested()) {
+    int64_t size;
+    rv = metadata->GetSize(&size);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    NS_ENSURE_TRUE(size >= 0, NS_ERROR_FAILURE);
+
+    mParams->mSize = uint64_t(size);
+  }
+
+  if (mParams->LastModifiedRequested()) {
+    int64_t lastModified;
+    rv = metadata->GetLastModified(&lastModified);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    mParams->mLastModified = lastModified;
+  }
+
+  return NS_OK;
+}