Teach the IDL compiler about TreatNullAs=EmptyString

Source/bindings/scripts/code_generator_v8.pm

 # Copyright (C) 2005, 2006 Nikolas Zimmermann <zimmermann@kde.org>
 # Copyright (C) 2006 Anders Carlsson <andersca@mac.com>
 # Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
 # Copyright (C) 2006 Alexey Proskuryakov <ap@webkit.org>
 # Copyright (C) 2006 Apple Computer, Inc.
 # Copyright (C) 2007, 2008, 2009, 2012 Google Inc.
 # Copyright (C) 2009 Cameron McCormack <cam@mcc.id.au>
 # Copyright (C) Research In Motion Limited 2010. All rights reserved.
 # Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
 # Copyright (C) 2012 Ericsson AB. All rights reserved.
@@ skipping 658 matching lines @@
         }
     }
 
     return 0;
 }
 
 sub GetV8StringResourceMode
 {
     my $extendedAttributes = shift;
 
-    # Blink uses the non-standard identifier NullString instead of Web IDL
-    # standard EmptyString, in [TreatNullAs=NullString] and [TreatUndefinedAs=NullString],
-    # and does not support [TreatUndefinedAs=Null] or [TreatUndefinedAs=Missing]
+    # In addition to [TreatNullAs=EmptyString], Blink also supports the non-standard
+    # [TreatNullAs=NullString] and formerly-standard [TreatUndefinedAs=NullString].
     # https://sites.google.com/a/chromium.org/dev/blink/webidl/blink-idl-extended-attributes#TOC-TreatNullAs-a-p-TreatUndefinedAs-a-p-
     my $mode = "";
-    if (($extendedAttributes->{"TreatNullAs"} and $extendedAttributes->{"TreatNullAs"} eq "NullString") and ($extendedAttributes->{"TreatUndefinedAs"} and $extendedAttributes->{"TreatUndefinedAs"} eq "NullString")) {
+    if ($extendedAttributes->{"TreatNullAs"} and $extendedAttributes->{"TreatNullAs"} eq "EmptyString") {
+        $mode = "TreatNullAsEmptyString";
+    } elsif (($extendedAttributes->{"TreatNullAs"} and $extendedAttributes->{"TreatNullAs"} eq "NullString") and ($extendedAttributes->{"TreatUndefinedAs"} and $extendedAttributes->{"TreatUndefinedAs"} eq "NullString")) {
         $mode = "WithUndefinedOrNullCheck";
     } elsif ($extendedAttributes->{"TreatNullAs"} and $extendedAttributes->{"TreatNullAs"} eq "NullString") {
         $mode = "WithNullCheck";
     }
     return $mode;
 }
 
 sub GenerateHeader
 {
     my $object = shift;
@@ skipping 5696 matching lines @@
         if ($parameter->type eq "SerializedScriptValue") {
             return 1;
         } elsif (IsIntegerType($parameter->type)) {
             return 1;
         }
     }
     return 0;
 }
 
 1;