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 (!properties.parseBlobPropertyBag(info[2], "File", info.GetIsolate()))
             return;
+    } else {
+        properties.setDefaultLastModifiedDate();
     }
 
     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());
 }
 
+void V8File::lastModifiedDateAttributeGetterCustom(const v8::PropertyCallbackInfo<v8::Value>& info)
+{
+    // The auto-generated getters return null when the method in the underlying
+    // implementation returns NaN. Here, we need to return a Date whose value
+    // is NaN when the File constructor receives such a Date. WebIDL calls it
+    // an "undefined date". Fortunately, lastModifiedDate never needs to return
+    // null, so we can get away with mapping NaN to "new Date(NaN)" instead of
+    // "null".
+    //
+    // See step 3.3 in Section 7.1, and Section 7.2 of the File API spec:
+    // http://dev.w3.org/2006/webapi/FileAPI/
+    //
+    // See the following sections of the WebIDL ED:
+    // 3.10.26: http://heycam.github.io/webidl/#idl-Date
+    // 4.2.27: http://heycam.github.io/webidl/#es-Date
+
+    File* file = V8File::toNative(info.Holder());
+    v8SetReturnValue(info, v8::Date::New(file->lastModifiedDate()));
+}
+
 } // namespace WebCore