Fix running "gen gn --args='target_os="ios"'".

ui/resources/BUILD.gn

 # 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("//tools/grit/grit_rule.gni")
 import("//tools/grit/repack.gni")
 
 # GYP version: ui/resources/ui_resources.gyp:ui_resources
 group("resources") {
   deps = [
@@ skipping 89 matching lines @@
   if (is_chromeos) {
     sources += [
       "$root_gen_dir/ui/chromeos/resources/ui_chromeos_resources_100_percent.pak",
       "$root_gen_dir/ui/chromeos/strings/ui_chromeos_strings_en-US.pak",
     ]
   }
 
   output = "$root_out_dir/ui_test.pak"
 
   deps = [
-    "//third_party/WebKit/public:resources_grit",
     "//ui/resources",
     "//ui/strings",
   ]
 
+  if (!is_ios) {
+    deps += [ "//third_party/WebKit/public:resources_grit" ]
+  }
+
   if (!is_mac) {
     deps += [ ":copy_ui_resources_100_percent" ]
   }
 
   if (is_chromeos) {
     deps += [
       "//ui/chromeos/resources",
       "//ui/chromeos/strings",
     ]
   }
@@ skipping 21 matching lines @@
     "$root_gen_dir/ui/strings/app_locale_settings_en-US.pak",
     "$root_gen_dir/ui/strings/ui_strings_en-US.pak",
   ]
 
   output = "$root_out_dir/ui/en.lproj/locale.pak"
 
   deps = [
     "//ui/strings",
   ]
 }