IDL build: factor out global objects action into a GYP template

Source/bindings/scripts/global_objects.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.
+#
+# This file is meant to be included into a target to provide an action
+# to compute global objects in a component.
+#
+# To use this, create a gyp target with the following form:
+# {
+#   'target_name': 'component_global_objects',
+#   'variables': {
+#     'idl_files': '<(list_of_idl_files)',
+#     'input_files': ['<(some_dir)/GlobalObjectBaseComponent.pickle'],
+#     'output_file': '<(some_dir)/GlobalObjectsComponent.pickle',
+#   },
+#   'includes': ['path/to/this/gypi/file'],
+# },
+#
+# Required variables:
+#  idl_files - List of .idl files that will be searched in.
+#    This should *only* contain main IDL files, excluding dependencies and
+#    testing, which should not define global objects).
+#  output_file - Pickle file of output.
+#
+# Optional variables:
+#  input_files - List of input pickle files of global objects in base
+#    components. In this case make sure to include a dependencies section
+#    in the target to ensure this is generated.
+#
+# Spec: http://heycam.github.io/webidl/#Global
+# Design document: http://www.chromium.org/developers/design-documents/idl-build
+
+{
+  'type': 'none',
+  'actions': [{
+    'action_name': 'compute_<(_target_name)',
+    'message': 'Computing global objects for <(_target_name)',
+    'variables': {
+      'input_files%': [],
+      'idl_files_list': '<|(idl_files_list.tmp <@(idl_files))',
+    },
+    'includes': ['scripts.gypi'],
+    'inputs': [
+      '<(bindings_scripts_dir)/compute_global_objects.py',
+      '<(bindings_scripts_dir)/utilities.py',
+      '<(idl_files_list)',
+      '<@(idl_files)',
+    ],
+    'outputs': [
+      '<(output_file)',
+    ],
+    'action': [
+      'python',
+      '<(bindings_scripts_dir)/compute_global_objects.py',
+      '--idl-files-list',
+      '<(idl_files_list)',
+      '--write-file-only-if-changed',
+      '<(write_file_only_if_changed)',
+      '--',
+      '<@(input_files)',
+      '<(output_file)',
+     ],
+  }],
+}