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

ios/chrome/browser/ui/history/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("history") {
   configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
     "clear_browsing_bar.h",
     "clear_browsing_bar.mm",
     "favicon_view.h",
@@ skipping 73 matching lines @@
     "//url",
   ]
   libs = [
     "MobileCoreServices.framework",
     "QuartzCore.framework",
     "UIKit.framework",
   ]
 }
 
 source_set("unit_tests") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true
   sources = [
     "favicon_view_provider_unittest.mm",
     "history_entries_status_item_unittest.mm",
     "history_entry_inserter_unittest.mm",
     "history_entry_item_unittest.mm",
     "history_search_view_controller_unittest.mm",
     "history_util_unittest.mm",
     "tab_history_popup_controller_unittest.mm",
   ]
@@ skipping 118 matching lines @@
     "//ios/third_party/earl_grey",
     "//ios/web:test_support",
     "//net",
     "//ui/base",
   ]
   libs = [
     "UIKit.framework",
     "XCTest.framework",
   ]
 }