IDL: make optional arguments (without default) explicit sometimes

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 198 matching lines @@
         return m_snapshotSize;
 
     // FIXME: JavaScript cannot represent sizes as large as unsigned long long, we need to
     // come up with an exception to throw if file size is not representable.
     long long size;
     if (!hasBackingFile() || !getFileSize(m_path, size))
         return 0;
     return static_cast<unsigned long long>(size);
 }
 
-PassRefPtrWillBeRawPtr<Blob> File::slice(long long start, long long end, const String& contentType, ExceptionState& exceptionState) const
+PassRefPtrWillBeRawPtr<Blob> File::slice(long long start, Optional<long long> optionalEnd, const String& contentType, ExceptionState& exceptionState) const
 {
     if (hasBeenClosed()) {
         exceptionState.throwDOMException(InvalidStateError, "File has been closed.");
         return nullptr;
     }
 
     if (!m_hasBackingFile)
-        return Blob::slice(start, end, contentType, exceptionState);
+        return Blob::slice(start, optionalEnd, contentType, exceptionState);
+
+    long long end = optionalEnd.isMissing() ? std::numeric_limits<long long>::max() : optionalEnd.get();
 
     // FIXME: This involves synchronous file operation. We need to figure out how to make it asynchronous.
     long long size;
     double modificationTime;
     captureSnapshot(size, modificationTime);
     clampSliceOffsets(size, start, end);
 
     long long length = end - start;
     OwnPtr<BlobData> blobData = BlobData::create();
     blobData->setContentType(contentType);
@@ skipping 58 matching lines @@
     captureSnapshot(size, modificationTime);
     if (!m_fileSystemURL.isEmpty()) {
         blobData.appendFileSystemURL(m_fileSystemURL, 0, size, modificationTime);
         return;
     }
     ASSERT(!m_path.isEmpty());
     blobData.appendFile(m_path, 0, size, modificationTime);
 }
 
 } // namespace blink