File constructor understands lastModified.

Source/core/fileapi/File.cpp

 /*
  * 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 143 matching lines @@
     , m_hasBackingFile(true)
     , m_fileSystemURL(fileSystemURL)
     , m_snapshotSize(metadata.length)
     , m_snapshotModificationTime(metadata.modificationTime)
 {
     ScriptWrappable::init(this);
 }
 
 double File::lastModifiedDate() const
 {
-    if (hasValidSnapshotMetadata() && isValidFileTime(m_snapshotModificationTime))
+    if (hasValidSnapshotMetadata())
         return m_snapshotModificationTime * msPerSecond;
 
     time_t modificationTime;
     if (getFileModificationTime(m_path, modificationTime) && isValidFileTime(modificationTime))
         return modificationTime * msPerSecond;
 
     return currentTime() * msPerSecond;
 }
 
 unsigned long long File::size() const
@@ skipping 24 matching lines @@
         snapshotSize = 0;
         snapshotModificationTime = invalidFileTime();
         return;
     }
 
     snapshotSize = metadata.length;
     snapshotModificationTime = metadata.modificationTime;
 }
 
 } // namespace WebCore