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

ios/chrome/browser/ui/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/ios/rules.gni")
 
 source_set("ui") {
   sources = [
     "UIView+SizeClassSupport.h",
     "UIView+SizeClassSupport.mm",
@@ skipping 41 matching lines @@
   allow_circular_includes_from = [ "//ios/chrome/browser/ui/commands" ]
   libs = [
     "Accelerate.framework",
     "CoreGraphics.framework",
     "QuartzCore.framework",
   ]
   configs += [ "//build/config/compiler:enable_arc" ]
 }
 
 source_set("unit_tests") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true
   sources = [
     "browser_container_view_unittest.mm",
     "browser_view_controller_unittest.mm",
     "chrome_web_view_factory_unittest.mm",
     "file_locations_unittest.mm",
     "fullscreen_controller_unittest.mm",
     "key_commands_provider_unittest.mm",
     "native_content_controller_unittest.mm",
     "network_activity_indicator_manager_unittest.mm",
@@ skipping 502 matching lines @@
     "//ios/chrome/browser/web_state_list",
     "//ios/chrome/browser/web_state_list:test_support",
     "//ios/chrome/test/base:perf_test_support",
     "//ios/web/public/test/fakes",
     "//testing/gtest",
     "//third_party/ocmock",
     "//ui/base:test_support",
   ]
   libs = [ "UIKit.framework" ]
 }