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

ios/chrome/browser/ui/toolbar/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.
 
 bundle_data("resources") {
   sources = [
     "resources/collapse.png",
     "resources/collapse@2x.png",
     "resources/collapse@3x.png",
     "resources/collapse_incognito.png",
@@ skipping 133 matching lines @@
   deps = [
     ":toolbar",
     "//base",
     "//components/toolbar",
     "//components/toolbar:test_support",
     "//ios/chrome/browser/tabs",
   ]
 }
 
 source_set("unit_tests") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true
   sources = [
     "toolbar_controller_unittest.mm",
     "toolbar_model_impl_ios_unittest.mm",
     "web_toolbar_controller_unittest.mm",
   ]
   deps = [
     ":test_support",
     ":toolbar",
     "//base",
@@ skipping 35 matching lines @@
     "//ios/chrome/browser/ui/tools_menu",
     "//ios/chrome/test/app:test_support",
     "//ios/chrome/test/earl_grey:test_support",
     "//ios/testing/earl_grey:earl_grey_support",
     "//ios/third_party/earl_grey",
     "//ios/web:test_support",
     "//ui/base",
   ]
   libs = [ "XCTest.framework" ]
 }