File constructor understands lastModified.

Source/bindings/v8/custom/V8BlobCustom.cpp

 /*
  * Copyright (C) 2012 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 37 matching lines @@
     if (info[0]->IsArray()) {
         length = v8::Local<v8::Array>::Cast(info[0])->Length();
     } else {
         const int sequenceArgumentIndex = 0;
         if (toV8Sequence(info[sequenceArgumentIndex], length, info.GetIsolate()).IsEmpty()) {
             throwTypeError(ExceptionMessages::failedToConstruct("Blob", ExceptionMessages::notAnArrayTypeArgumentOrValue(sequenceArgumentIndex + 1)), info.GetIsolate());
             return;
         }
     }
 
-    String contentType;
-    String endings = "transparent"; // default if no BlobPropertyBag is passed
+    V8BlobCustomHelpers::ParsedProperties properties(false);
     if (info.Length() > 1) {
         if (!info[1]->IsObject()) {
             throwTypeError(ExceptionMessages::failedToConstruct("Blob", "The 2nd argument is not of type Object."), info.GetIsolate());
             return;
         }
 
-        if (!V8BlobCustomHelpers::processBlobPropertyBag(info[1], "Blob", contentType, endings, info.GetIsolate()))
+        if (!properties.parseBlobPropertyBag(info[1], "Blob", info.GetIsolate()))
             return;
     }
 
     BlobBuilder blobBuilder;
     v8::Local<v8::Object> blobParts = v8::Local<v8::Object>::Cast(info[0]);
-    if (!V8BlobCustomHelpers::processBlobParts(blobParts, length, endings, blobBuilder, info.GetIsolate()))
+    if (!V8BlobCustomHelpers::processBlobParts(blobParts, length, properties.endings(), blobBuilder, info.GetIsolate()))
         return;
 
-    RefPtr<Blob> blob = blobBuilder.createBlob(contentType);
+    RefPtr<Blob> blob = blobBuilder.createBlob(properties.contentType());
     v8SetReturnValue(info, blob.release());
 }
 
 } // namespace WebCore