[ios] Convert //ios/chrome/browser/tabs:unit_tests to ARC.

ios/chrome/browser/tabs/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("tabs") {
   sources = [
     "legacy_tab_helper.h",
     "tab.h",
     "tab_delegate.h",
     "tab_dialog_delegate.h",
@@ skipping 124 matching lines @@
     "CoreLocation.framework",
     "Foundation.framework",
     "UIKit.framework",
   ]
   configs += [ "//build/config/compiler:enable_arc" ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
+    "tab_model_list_unittest.mm",
     "tab_model_unittest.mm",
     "tab_unittest.mm",
   ]
   deps = [
     ":tabs",
     ":tabs_internal",
-    ":unit_tests_arc",
     "//base",
     "//components/bookmarks/test",
     "//components/history/core/browser",
     "//components/keyed_service/core",
     "//ios/chrome/browser",
     "//ios/chrome/browser/bookmarks",
     "//ios/chrome/browser/browser_state:test_support",
     "//ios/chrome/browser/history",
     "//ios/chrome/browser/infobars",
     "//ios/chrome/browser/sessions",
     "//ios/chrome/browser/sessions:serialisation",
     "//ios/chrome/browser/sessions:test_support",
     "//ios/chrome/browser/ui:ui_internal",
     "//ios/chrome/browser/web:web_internal",
     "//ios/chrome/browser/web_state_list",
     "//ios/chrome/test:test_support",
     "//ios/public/provider/chrome/browser",
     "//ios/public/provider/chrome/browser:test_support",
     "//ios/public/provider/chrome/browser/native_app_launcher:test_support",
     "//ios/testing:ocmock_support",
     "//ios/web",
     "//ios/web:test_support",
     "//net",
     "//testing/gtest",
     "//third_party/ocmock",
   ]
-}
-
-source_set("unit_tests_arc") {
-  testonly = true
-  sources = [
-    "tab_model_list_unittest.mm",
-  ]
-  deps = [
-    ":tabs",
-    ":tabs_internal",
-    "//base",
-    "//ios/chrome/browser/browser_state:test_support",
-    "//ios/chrome/browser/sessions:test_support",
-    "//ios/web:test_support",
-    "//testing/gtest",
-  ]
   configs += [ "//build/config/compiler:enable_arc" ]
 }