IDL: Use Nullable for union type return value

Source/bindings/scripts/v8_methods.py

Index: Source/bindings/scripts/v8_methods.py
diff --git a/Source/bindings/scripts/v8_methods.py b/Source/bindings/scripts/v8_methods.py
index c69fcd1f3bec6af9e2d387395ce9e368fa0ed1a7..2dff48b00498b23a56ce8dc294288474bfa05903 100644
--- a/Source/bindings/scripts/v8_methods.py
+++ b/Source/bindings/scripts/v8_methods.py
@@ -304,7 +304,8 @@ def cpp_value(interface, method, number_of_arguments):
 
     this_union_arguments = method.idl_type and method.idl_type.union_arguments
     if this_union_arguments:
-        cpp_arguments.extend(this_union_arguments)
+        cpp_arguments.extend([member_argument['cpp_value']
+                              for member_argument in this_union_arguments])
 
     if 'ImplementedInPrivateScript' in method.extended_attributes:
         if method.idl_type.name != 'void':
@@ -401,11 +402,35 @@ def property_attributes(method):
     return property_attributes_list
 
 
+def union_member_argument_context(idl_type, index):
+    """Returns a context of union member for argument."""
+    this_cpp_value = 'result%d' % index
+    this_cpp_type = idl_type.cpp_type
+    cpp_return_value = this_cpp_value
+
+    if not idl_type.cpp_type_has_null_value:
+        this_cpp_type = v8_types.cpp_template_type('Nullable', this_cpp_type)
+        cpp_return_value = '%s.get()' % this_cpp_value
+
+    if idl_type.is_string_type:
+        null_check_value = '!%s.isNull()' % this_cpp_value
+    else:
+        null_check_value = this_cpp_value
+
+    return {
+        'cpp_type': this_cpp_type,
+        'cpp_value': this_cpp_value,
+        'null_check_value': null_check_value,
+        'v8_set_return_value': idl_type.v8_set_return_value(
+            cpp_value=cpp_return_value,
+            release=idl_type.release),
+    }
+
+
 def union_arguments(idl_type):
-    """Return list of ['result0Enabled', 'result0', 'result1Enabled', ...] for union types, for use in setting return value"""
-    return [arg
-            for i in range(len(idl_type.member_types))
-            for arg in ['result%sEnabled' % i, 'result%s' % i]]
+    return [union_member_argument_context(member_idl_type, index)
+            for index, member_idl_type
+            in enumerate(idl_type.member_types)]
 
 
 def argument_default_cpp_value(argument):