Fixed WebDragData's wrong dependency.

Source/core/clipboard/DraggedIsolatedFileSystem.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef DraggedIsolatedFileSystem_h
+#define DraggedIsolatedFileSystem_h
+
+#include "platform/heap/Handle.h"
+#include "wtf/Forward.h"
+
+namespace blink {
+
+class DataObject;
+
+class DraggedIsolatedFileSystem {
+    WTF_MAKE_NONCOPYABLE(DraggedIsolatedFileSystem);
+public:
+    DraggedIsolatedFileSystem() { }
+    virtual ~DraggedIsolatedFileSystem() { }
+
+    using FileSystemIdPreparationCallback = void(*)(DataObject*, const String&);
+    static void init(FileSystemIdPreparationCallback);
+
+    static void prepareForDataObject(DataObject*, const String& filesystemId);
+
+private:
+    static FileSystemIdPreparationCallback s_prepareCallback;
+};
+
+} // namespace blink
+
+#endif // DraggedIsolatedFileSystem_h