IDL: Generate union type containers

Source/bindings/modules/v8/generated.gypi

 # 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.
 
 {
   'variables': {
     'bindings_modules_v8_output_dir': '<(SHARED_INTERMEDIATE_DIR)/blink/bindings/modules/v8',
+    'bindings_modules_v8_generated_union_type_files': [
+      # FIXME: Uncomment following entries when we start using union types in modules.
+      #'<(bindings_modules_v8_output_dir)/UnionTypesModules.cpp',
+      #'<(bindings_modules_v8_output_dir)/UnionTypesModules.h',
+    ],
 
     'conditions': [
       ['OS=="win" and buildtype=="Official"', {
         # On Windows Official release builds, we try to preserve symbol
         # space.
         'bindings_modules_v8_generated_aggregate_files': [
           '<(bindings_modules_v8_output_dir)/V8GeneratedModulesBindings.cpp',
         ],
       }, {
         'bindings_modules_v8_generated_aggregate_files': [
@@ skipping 17 matching lines @@
           '<(bindings_modules_v8_output_dir)/V8GeneratedModulesBindings18.cpp',
           '<(bindings_modules_v8_output_dir)/V8GeneratedModulesBindings19.cpp',
         ],
       }],
     ],
     'bindings_modules_v8_generated_partial_aggregate_files': [
       '<(bindings_modules_v8_output_dir)/V8GeneratedModulesBindingsPartial.cpp',
     ],
   },
 }