Make Blob constructor's first argument optional.

third_party/WebKit/Source/core/fileapi/Blob.idl

 /*
  * 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 13 matching lines @@
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 // https://w3c.github.io/FileAPI/#blob
 
 [
-    Constructor,
-    Constructor(sequence<(ArrayBuffer or ArrayBufferView or Blob or DOMString)> blobParts, optional BlobPropertyBag options),
+    Constructor(optional sequence<(ArrayBuffer or ArrayBufferView or Blob or DOMString)> blobParts, optional BlobPropertyBag options),
     RaisesException=Constructor,
     Exposed=(Window,Worker),
 ] interface Blob {
     readonly attribute unsigned long long size;
     readonly attribute DOMString type;
     // TODO(jsbell): Implement:
     // readonly attribute boolean isClosed;
 
     // TODO(jsbell): start and end arguments should be [Clamp]
     // TODO(philipj): contentType should not be optional or nullable.
     [RaisesException] Blob slice(optional long long start, optional long long end, [TreatUndefinedAs=NullString] optional DOMString? contentType);
     [RaisesException, CallWith=ExecutionContext, RuntimeEnabled=FileAPIBlobClose] void close();
 };