Add gn template for vector icon actions.

ash/resources/vector_icons/BUILD.gn

 # Copyright 2016 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.
 
-action("aggregate_vector_icons") {
-  visibility = [ ":*" ]
+import("//ui/vector_icons/vector_icons.gni")
 
-  script = "//ui/gfx/vector_icons/aggregate_vector_icons.py"
+aggregate_vector_icons("ash_vector_icons") {
+  icon_directory = "."
 
   icons = [
     "ime_menu_emoticon.1x.icon",
     "ime_menu_emoticon.icon",
     "ime_menu_microphone.1x.icon",
     "ime_menu_microphone.icon",
     "ime_menu_on_screen_keyboard.1x.icon",
     "ime_menu_on_screen_keyboard.icon",
     "ime_menu_write.1x.icon",
     "ime_menu_write.icon",
@@ skipping 198 matching lines @@
     "window_control_left_snapped.icon",
     "window_control_maximize.1x.icon",
     "window_control_maximize.icon",
     "window_control_minimize.1x.icon",
     "window_control_minimize.icon",
     "window_control_restore.1x.icon",
     "window_control_restore.icon",
     "window_control_right_snapped.1x.icon",
     "window_control_right_snapped.icon",
   ]
-
-  output_cc = "$target_gen_dir/vector_icons.cc"
-  output_h = "$target_gen_dir/vector_icons.h"
-
-  inputs = icons
-  inputs += [
-    "vector_icons.cc.template",
-    "vector_icons.h.template",
-  ]
-  outputs = [
-    output_cc,
-    output_h,
-  ]
-
-  response_file_contents = rebase_path(icons, root_build_dir)
-
-  args = [
-    "--working_directory=" + rebase_path("./"),
-    "--file_list={{response_file_name}}",
-    "--output_cc=" + rebase_path(output_cc, root_build_dir),
-    "--output_h=" + rebase_path(output_h, root_build_dir),
-  ]
 }
 
 source_set("vector_icons") {
-  sources = get_target_outputs(":aggregate_vector_icons")
+  sources = get_target_outputs(":ash_vector_icons")
   sources += [ "//ui/gfx/vector_icon_types.h" ]
 
   deps = [
-    ":aggregate_vector_icons",
+    ":ash_vector_icons",
     "//base",
     "//skia",
   ]
 }