IDL: make optional arguments (without default) explicit sometimes

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 86 matching lines @@
     }
 
     static PassRefPtrWillBeRawPtr<File> createForFileSystemFile(const String& path, const String& name, ContentTypeLookupPolicy policy = WellKnownContentTypes)
     {
         if (name.isEmpty())
             return adoptRefWillBeNoop(new File(path, policy, File::IsNotUserVisible));
         return adoptRefWillBeNoop(new File(path, name, policy, File::IsNotUserVisible));
     }
 
     virtual unsigned long long size() const OVERRIDE;
-    virtual PassRefPtrWillBeRawPtr<Blob> slice(long long start, long long end, const String& contentType, ExceptionState&) const OVERRIDE;
+    virtual PassRefPtrWillBeRawPtr<Blob> slice(long long start, Optional<long long> end, const String& contentType, ExceptionState&) const OVERRIDE;
     virtual void close(ExecutionContext*, ExceptionState&) OVERRIDE;
 
     virtual bool isFile() const OVERRIDE { return true; }
     virtual bool hasBackingFile() const OVERRIDE { return m_hasBackingFile; }
 
     virtual void appendTo(BlobData&) const OVERRIDE;
 
     const String& path() const { ASSERT(hasValidFilePath()); return m_path; }
     const String name() const { return m_name; }
 
@@ skipping 49 matching lines @@
     const double m_snapshotModificationTime;
 
     String m_relativePath;
 };
 
 DEFINE_TYPE_CASTS(File, Blob, blob, blob->isFile(), blob.isFile());
 
 } // namespace blink
 
 #endif // File_h