Implement platform deleters per spec.

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 4055 matching lines @@
     my $implClassName = GetImplName($interface);
     my $v8ClassName = GetV8ClassName($interface);
     my $methodName = GetImplName($namedDeleterFunction);
 
     my $raisesExceptions = $namedDeleterFunction->extendedAttributes->{"RaisesException"};
 
     my $code = "static void namedPropertyDeleter(v8::Local<v8::String> name, const v8::PropertyCallbackInfo<v8::Boolean>& info)\n";
     $code .= "{\n";
     $code .= "    ${implClassName}* collection = ${v8ClassName}::toNative(info.Holder());\n";
     $code .= "    AtomicString propertyName = toCoreAtomicString(name);\n";
-    my $extraArguments = "";
+    my $extraArguments = ", result";
     if ($raisesExceptions) {
         $code .= "    ExceptionState exceptionState(info.Holder(), info.GetIsolate());\n";
-        $extraArguments = ", exceptionState";
+        $extraArguments .= ", exceptionState";
     }
-    $code .= "    bool result = collection->${methodName}(propertyName$extraArguments);\n";
+    $code .= "    bool result = true;\n";
+    $code .= "    bool knownProperty = collection->${methodName}(propertyName$extraArguments);\n";
     if ($raisesExceptions) {
         $code .= "    if (exceptionState.throwIfNeeded())\n";
         $code .= "        return;\n";
     }
-    $code .= "    return v8SetReturnValueBool(info, result);\n";
+    $code .= "    if (knownProperty)\n";
+    $code .= "        return v8SetReturnValueBool(info, result);\n";
     $code .= "}\n\n";
     $implementation{nameSpaceInternal}->add($code);
 }
 
 sub GenerateImplementationNamedPropertyEnumerator
 {
     my $interface = shift;
     my $implClassName = GetImplName($interface);
     my $v8ClassName = GetV8ClassName($interface);
 
@@ skipping 2240 matching lines @@
 
     return 1 if ExtendedAttributeContains($interface->extendedAttributes->{"Custom"}, "ToV8");
     return 1 if ExtendedAttributeContains($interface->extendedAttributes->{"Custom"}, "Wrap");
     return 1 if $interface->extendedAttributes->{"SpecialWrapFor"};
     return 1 if InheritsInterface($interface, "Document");
 
     return 0;
 }
 
 1;