IDL: Support optional union type arguments with default values

Source/bindings/scripts/v8_union.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import v8_utilities
 
 
 UNION_H_INCLUDES = frozenset([
     'bindings/core/v8/ExceptionState.h',
     'bindings/core/v8/V8Binding.h',
@@ skipping 56 matching lines @@
         elif member.base_type == 'ArrayBufferView':
             if array_buffer_view_type:
                 raise Exception('%s is ambiguous.' % union_type.name)
             array_buffer_view_type = context
         elif member.is_interface_type:
             interface_types.append(context)
         elif member.is_dictionary:
             if dictionary_type:
                 raise Exception('%s is ambiguous.' % union_type.name)
             dictionary_type = context
-        elif member.base_type == 'boolean':
-            if boolean_type:
-                raise Exception('%s is ambiguous.' % union_type.name)
+        elif member is union_type.boolean_member_type:
             boolean_type = context
-        elif member.is_numeric_type:
-            if numeric_type:
-                raise Exception('%s is ambiguous.' % union_type.name)
+        elif member is union_type.numeric_member_type:
             numeric_type = context
-        elif member.is_string_type:
-            if string_type:
-                raise Exception('%s is ambiguous.' % union_type.name)
+        elif member is union_type.string_member_type:
             string_type = context
         else:
             raise Exception('%s is not supported as an union member.' % member.name)
 
     # Nullable restriction checks
     nullable_members = union_type.number_of_nullable_member_types
     if nullable_members > 1:
         raise Exception('%s contains more than one nullable members' % union_type.name)
     if dictionary_type and nullable_members == 1:
         raise Exception('%s has a dictionary and a nullable member' % union_type.name)
@@ skipping 28 matching lines @@
         'cpp_value_to_v8_value': member.cpp_value_to_v8_value(
             cpp_value='impl.getAs%s()' % member.name, isolate='isolate',
             creation_context='creationContext'),
         'is_traceable': member.is_traceable,
         'rvalue_cpp_type': member.cpp_type_args(used_as_rvalue_type=True),
         'specific_type_enum': 'SpecificType' + member.name,
         'type_name': member.name,
         'v8_value_to_local_cpp_value': member.v8_value_to_local_cpp_value(
             {}, 'v8Value', 'cppValue', needs_exception_state_for_string=True),
     }