IDL: make optional arguments (without default) explicit sometimes

Source/core/fileapi/Blob.cpp

 /*
  * Copyright (C) 2010 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 88 matching lines @@
         end = 0;
     if (start >= size) {
         start = 0;
         end = 0;
     } else if (end < start)
         end = start;
     else if (end > size)
         end = size;
 }
 
-PassRefPtrWillBeRawPtr<Blob> Blob::slice(long long start, long long end, const String& contentType, ExceptionState& exceptionState) const
+PassRefPtrWillBeRawPtr<Blob> Blob::slice(long long start, Optional<long long> optionalEnd, const String& contentType, ExceptionState& exceptionState) const
 {
     if (hasBeenClosed()) {
         exceptionState.throwDOMException(InvalidStateError, "Blob has been closed.");
         return nullptr;
     }
 
+    long long end = optionalEnd.isMissing() ? std::numeric_limits<long long>::max() : optionalEnd.get();
+
     long long size = this->size();
     clampSliceOffsets(size, start, end);
 
     long long length = end - start;
     OwnPtr<BlobData> blobData = BlobData::create();
     blobData->setContentType(contentType);
     blobData->appendBlob(m_blobDataHandle, start, length);
     return Blob::create(BlobDataHandle::create(blobData.release(), length));
 }
 
@@ skipping 23 matching lines @@
 {
     blobData.appendBlob(m_blobDataHandle, 0, m_blobDataHandle->size());
 }
 
 URLRegistry& Blob::registry() const
 {
     return BlobURLRegistry::registry();
 }
 
 } // namespace blink