Implement platform deleters per spec.

Source/bindings/scripts/code_generator_v8.pm

Index: Source/bindings/scripts/code_generator_v8.pm
diff --git a/Source/bindings/scripts/code_generator_v8.pm b/Source/bindings/scripts/code_generator_v8.pm
index a0a5565bfee9821123c4808b9a22969be0671c31..2fa8397b148a89b13badcd8e07b3ba78c0811dd7 100644
--- a/Source/bindings/scripts/code_generator_v8.pm
+++ b/Source/bindings/scripts/code_generator_v8.pm
@@ -4073,17 +4073,19 @@ sub GenerateImplementationNamedPropertyDeleter
     $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);
 }