Asynchronously loads the given URL as a blob. Returns a promise that will resolve to a Blob once loaded, or reject if the URL failed to load. The data is loaded using XMLHttpRequest, which means that in order to make requests to another origin, the server must have Cross-Origin Resource Sharing (CORS) headers enabled.
|The URL of the data.
|optional HTTP headers to send with the requests.
|optional The request object. Intended for internal use only.
a promise that will resolve to the requested data when loaded. Returns undefined if
request.throttle is true and the request does not have high enough priority.