[ObjC ARC] Converts ios/chrome/browser/ui/static_content:unit_tests to ARC.

ios/chrome/browser/ui/static_content/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.
 
 source_set("static_content") {
   sources = [
     "static_html_native_content.h",
     "static_html_native_content.mm",
     "static_html_view_controller.h",
     "static_html_view_controller.mm",
   ]
   deps = [
     "//base",
     "//ios/chrome/browser/ui",
     "//ios/web",
     "//net",
     "//ui/base",
   ]
 }
 
 source_set("unit_tests") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true
   sources = [
     "static_html_native_content_unittest.mm",
     "static_html_view_controller_unittest.mm",
   ]
   deps = [
     ":static_content",
     "//base",
     "//base/test:test_support",
     "//ios/chrome/app/strings",
     "//ios/chrome/browser/browser_state:test_support",
     "//ios/chrome/browser/ui",
     "//ios/testing:ocmock_support",
     "//ios/web",
     "//ios/web:test_support",
     "//net",
     "//testing/gtest",
     "//third_party/ocmock",
     "//ui/base",
   ]
 }