Fix the hasBackingFile flag for File backed by a file system URL.

Source/core/fileapi/File.h

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 132 matching lines @@
     File(const String& name, const FileMetadata&, UserVisibility);
     File(const KURL& fileSystemURL, const FileMetadata&);
 
     void invalidateSnapshotMetadata() { m_snapshotSize = -1; }
 
     // Returns File's last modified time (in MS since Epoch.)
     // If the modification time isn't known, the current time is returned.
     double lastModifiedMS() const;
 
 #if ENABLE(ASSERT)
-    bool hasValidFileSystemURL() const { return hasBackingFile(); }
+    // Instances backed by a file must have an empty file system URL.
+    bool hasValidFileSystemURL() const { return !hasBackingFile() || m_fileSystemURL.isEmpty(); }
     // Instances not backed by a file must have an empty path set.
     bool hasValidFilePath() const { return hasBackingFile() || m_path.isEmpty(); }
 #endif
 
     bool m_hasBackingFile;
     UserVisibility m_userVisibility;
     String m_path;
     String m_name;
 
     KURL m_fileSystemURL;
 
     // If m_snapshotSize is negative (initialized to -1 by default), the snapshot metadata is invalid and we retrieve the latest metadata synchronously in size(), lastModifiedTime() and slice().
     // Otherwise, the snapshot metadata are used directly in those methods.
     long long m_snapshotSize;
     const double m_snapshotModificationTime;
 
     String m_relativePath;
 };
 
 DEFINE_TYPE_CASTS(File, Blob, blob, blob->isFile(), blob.isFile());
 
 } // namespace blink
 
 #endif // File_h