IDL: make optional arguments (without default) explicit sometimes

Source/core/fileapi/Blob.cpp

Index: Source/core/fileapi/Blob.cpp
diff --git a/Source/core/fileapi/Blob.cpp b/Source/core/fileapi/Blob.cpp
index 0363fa818ec3a6f4c9ce0572d093c1d6948b4109..d2f02eb4d8b93a719c6b62f05b17725da1de40ba 100644
--- a/Source/core/fileapi/Blob.cpp
+++ b/Source/core/fileapi/Blob.cpp
@@ -106,13 +106,15 @@ void Blob::clampSliceOffsets(long long size, long long& start, long long& end)
         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);