File constructor understands lastModified.

Source/bindings/v8/custom/V8FileCustom.cpp

 /*
  * Copyright (C) 2013 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 44 matching lines @@
     } else {
         const int sequenceArgumentIndex = 0;
         if (toV8Sequence(info[sequenceArgumentIndex], length, info.GetIsolate()).IsEmpty()) {
             throwTypeError(ExceptionMessages::failedToConstruct("File", ExceptionMessages::notAnArrayTypeArgumentOrValue(sequenceArgumentIndex + 1)), info.GetIsolate());
             return;
         }
     }
 
     V8TRYCATCH_FOR_V8STRINGRESOURCE_VOID(V8StringResource<>, fileName, info[1]);
 
-    String contentType;
-    String endings = "transparent"; // default if no BlobPropertyBag is passed
+    V8BlobCustomHelpers::ParsedProperties properties(true);
     if (info.Length() > 2) {
         if (!info[2]->IsObject()) {
             throwTypeError(ExceptionMessages::failedToConstruct("File", "The 3rd argument is not of type Object."), info.GetIsolate());
             return;
         }
 
-        if (!V8BlobCustomHelpers::processBlobPropertyBag(info[2], "File", contentType, endings, info.GetIsolate()))
+        if (!V8BlobCustomHelpers::processBlobPropertyBag(info[2], "File", properties, 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<File> file = blobBuilder.createFile(contentType, fileName, currentTime());
+    RefPtr<File> file = blobBuilder.createFile(properties.contentType, fileName, properties.lastModifiedDate());
     v8SetReturnValue(info, file.release());
 }
 
 } // namespace WebCore