Some of the functions in MIMETypeRegistry return HashSet<Sting>. For these functions, we need to do the following: 1. Use NeverDestroyed<> instead of allocating raw pointers with the new operator. 2. Use std::initializer_list to initialize the static HashSet<String> when the list of supported mime types is static list of strings. 3. Use makeNeverDestroyed() to initialize the static HashSet<String> when the list of supported mime types is retrieved from a system call. 3. Replace the functions MIMETypeRegistry::getSupported...() with MIMETypeRegistry::supported...(). The functions whose names are MIMETypeRegistry::supported...() will be responsible of filling and validating their local NeverDestroyed<> and returning the underlaying HashSets. 4. As a preparation for landing 190454, the term UTI will be replaced by ImageSourceType. A new SPI will be added and adding UTI in its name does not seem appealing.