Fix bug whereby booleans in unions could not be serialized in python.

mojo/public/tools/bindings/generators/mojom_python_generator.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.
 
 """Generates Python source files from a mojom.Module."""
 
 import re
 
 import mojom.generate.constant_resolver as resolver
 import mojom.generate.generator as generator
@@ skipping 157 matching lines @@
     return '_descriptor.InterfaceType(%s)' % ', '.join(arguments)
 
   if mojom.IsInterfaceRequestKind(kind):
     arguments = []
     if mojom.IsNullableKind(kind):
       arguments.append('nullable=True')
     return '_descriptor.InterfaceRequestType(%s)' % ', '.join(arguments)
 
   return _kind_to_type[kind]
 
-def GetFieldDescriptor(field, index, min_version):
+def GetFieldDescriptor(field, index, min_version, union_field=False):
   class_name = 'SingleFieldGroup'
-  if field.kind == mojom.BOOL:
+  if field.kind == mojom.BOOL and not union_field:
     class_name = 'FieldDescriptor'
   arguments = [ '%r' % GetNameForElement(field) ]
   arguments.append(GetFieldType(field.kind, field))
   arguments.append(str(index))
   arguments.append(str(min_version))
   if field.default:
     if mojom.IsStructKind(field.kind):
       arguments.append('default_value=True')
     else:
       arguments.append('default_value=%s' % ExpressionToText(field.default))
   return '_descriptor.%s(%s)' % (class_name, ', '.join(arguments))
 
 def GetStructFieldDescriptor(packed_field):
   return GetFieldDescriptor(
       packed_field.field, packed_field.index, packed_field.min_version)
 
 def GetUnionFieldDescriptor(field):
-  return GetFieldDescriptor(field, field.ordinal, 0)
+  return GetFieldDescriptor(field, field.ordinal, 0, union_field=True)
 
 def GetFieldGroup(byte):
   if byte.packed_fields[0].field.kind == mojom.BOOL:
     descriptors = map(GetStructFieldDescriptor, byte.packed_fields)
     return '_descriptor.BooleanGroup([%s])' % ', '.join(descriptors)
   assert len(byte.packed_fields) == 1
   return GetStructFieldDescriptor(byte.packed_fields[0])
 
 def MojomToPythonImport(mojom):
   return mojom.replace('.mojom', '_mojom')
@@ skipping 28 matching lines @@
   def GetImports(self):
     for each in self.module.imports:
       each['python_module'] = MojomToPythonImport(each['module_name'])
     return self.module.imports
 
   def GetJinjaParameters(self):
     return {
       'lstrip_blocks': True,
       'trim_blocks': True,
     }