diff -r 000000000000 -r 6474c204b198 dom/file/MetadataHelper.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/file/MetadataHelper.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,120 @@
+/* -*- 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/. */
+
+#ifndef mozilla_dom_file_metadatahelper_h__
+#define mozilla_dom_file_metadatahelper_h__
+
+#include "mozilla/Attributes.h"
+#include "FileCommon.h"
+
+#include "nsIFileStreams.h"
+
+#include "AsyncHelper.h"
+#include "FileHelper.h"
+
+class nsIFileStream;
+
+BEGIN_FILE_NAMESPACE
+
+class MetadataHelper;
+
+class MetadataParameters MOZ_FINAL
+{
+  friend class MetadataHelper;
+
+public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(MetadataParameters)
+
+  MetadataParameters(bool aSizeRequested, bool aLastModifiedRequested)
+    : mSizeRequested(aSizeRequested)
+    , mLastModifiedRequested(aLastModifiedRequested)
+  {
+  }
+
+  bool
+  IsConfigured() const
+  {
+    return mSizeRequested || mLastModifiedRequested;
+  }
+
+  bool
+  SizeRequested() const
+  {
+    return mSizeRequested;
+  }
+
+  bool
+  LastModifiedRequested() const
+  {
+    return mLastModifiedRequested;
+  }
+
+  uint64_t
+  Size() const
+  {
+    return mSize;
+  }
+
+  int64_t
+  LastModified() const
+  {
+    return mLastModified;
+  }
+
+private:
+  // Private destructor, to discourage deletion outside of Release():
+  ~MetadataParameters()
+  {
+  }
+
+  uint64_t mSize;
+  int64_t mLastModified;
+  bool mSizeRequested;
+  bool mLastModifiedRequested;
+};
+
+class MetadataHelper : public FileHelper
+{
+public:
+  MetadataHelper(LockedFile* aLockedFile,
+                 FileRequest* aFileRequest,
+                 MetadataParameters* aParams)
+  : FileHelper(aLockedFile, aFileRequest),
+    mParams(aParams)
+  { }
+
+  nsresult
+  DoAsyncRun(nsISupports* aStream) MOZ_OVERRIDE;
+
+  nsresult
+  GetSuccessResult(JSContext* aCx,
+                   JS::MutableHandle<JS::Value> aVal) MOZ_OVERRIDE;
+
+protected:
+  class AsyncMetadataGetter : public AsyncHelper
+  {
+  public:
+    AsyncMetadataGetter(nsISupports* aStream, MetadataParameters* aParams,
+                        bool aReadWrite)
+    : AsyncHelper(aStream),
+      mParams(aParams), mReadWrite(aReadWrite)
+    { }
+
+  protected:
+    nsresult
+    DoStreamWork(nsISupports* aStream) MOZ_OVERRIDE;
+
+  private:
+    nsRefPtr<MetadataParameters> mParams;
+    bool mReadWrite;
+  };
+
+  nsRefPtr<MetadataParameters> mParams;
+};
+
+END_FILE_NAMESPACE
+
+#endif // mozilla_dom_file_metadatahelper_h__