Implement python mojo bindings unions.

mojo/public/tools/bindings/generators/python_templates/module.py.tmpl

 {% from "module_macros.tmpl" import enum_values %}
 {% from "module_macros.tmpl" import struct_descriptor %}
+{% from "module_macros.tmpl" import union_descriptor %}
 # 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 mojo_bindings.descriptor as _descriptor
 import mojo_bindings.reflection as _reflection
 {% if interfaces %}
 import mojo_bindings.interface_reflection as _interface_reflection
 {% endif %}
 {% if imports %}
@@ skipping 14 matching lines @@
 class {{enum|name}}(object):
   __metaclass__ = _reflection.MojoEnumType
   VALUES = {{enum_values(enum)|indent(2)}}
 {% endfor %}
 {% for struct in structs %}
 
 class {{struct|name}}(object):
   __metaclass__ = _reflection.MojoStructType
   DESCRIPTOR = {{struct_descriptor(struct)|indent(2)}}
 {% endfor %}
+{% for union in unions %}
+
+class {{union|name}}(object):
+  __metaclass__ = _reflection.MojoUnionType
+  DESCRIPTOR = {{union_descriptor(union)|indent(2)}}
+{% endfor %}
+
 {% for interface in interfaces %}
 
 class {{interface|name}}(object):
   __metaclass__ = _interface_reflection.MojoInterfaceType
   DESCRIPTOR = {
     'fully_qualified_name': '{% if namespace %}{{namespace|replace(".","::")}}::{% endif %}{{interface|fully_qualified_name|replace(".","::")}}',
     'version': {{interface.version}},
     'methods': [
 {%  for method in interface.methods %}
       {
         'name': '{{method|name}}',
         'ordinal': {{method.ordinal}},
         'parameters': {{struct_descriptor(method.param_struct)|indent(8)}},
 {%    if method.response_parameters != None %}
         'responses': {{struct_descriptor(method.response_param_struct)|indent(8)}},
 {%    endif %}
       },
 {%  endfor %}
     ],
   }
 {% endfor %}