[iOS] Mark test bundle_data targets as testonly.

ui/gfx/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("//build/config/ui.gni")
 import("//testing/test.gni")
 
 if (is_android) {
   import("//build/config/android/config.gni")
   import("//build/config/android/rules.gni")
@@ skipping 672 matching lines @@
       "test/ui_cocoa_test_helper.h",
       "test/ui_cocoa_test_helper.mm",
     ]
   }
   if (is_linux) {
     deps += [ "//build/linux:fontconfig" ]
   }
 }
 
 bundle_data("gfx_unittests_bundle_data") {
+  testonly = true
   sources = [
     "test/data",
   ]
   outputs = [
     "{{bundle_resources_dir}}/" +
         "{{source_root_relative_dir}}/{{source_file_part}}",
   ]
 }
 
 test("gfx_unittests") {
@@ skipping 151 matching lines @@
 if (is_android) {
   generate_jni("gfx_jni_headers") {
     sources = [
       "../android/java/src/org/chromium/ui/gfx/BitmapHelper.java",
       "../android/java/src/org/chromium/ui/gfx/DeviceDisplayInfo.java",
       "../android/java/src/org/chromium/ui/gfx/ViewConfigurationHelper.java",
     ]
     jni_package = "gfx"
   }
 }