[iOS/GN] Define targets to application extensions resources.

ios/chrome/today_extension/strings/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.
+
+import("//build/config/locales.gni")
+import("//tools/grit/grit_rule.gni")
+
+grit("strings") {
+  source = "ios_today_extension_strings.grd"
+  output_dir = "$root_gen_dir/ios/today_extension"
+  use_qualified_include = true
+  outputs = [
+    "grit/ios_today_extension_strings.h",
+  ]
+  foreach(locale, locales_with_fake_bidi) {
+    outputs += [ "ios_today_extension_strings_$locale.pak" ]
+  }
+}