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

ios/chrome/browser/ui/infobars/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("infobars") {
   sources = [
     "infobar_view.h",
     "infobar_view.mm",
     "infobar_view_delegate.h",
   ]
@@ skipping 13 matching lines @@
     "//url",
   ]
   libs = [
     "CoreGraphics.framework",
     "QuartzCore.framework",
     "UIKit.framework",
   ]
 }
 
 source_set("unit_tests") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true
   sources = [
     "infobar_view_unittest.mm",
   ]
   deps = [
     ":infobars",
     "//testing/gtest",
   ]
 }
 
@@ skipping 34 matching lines @@
     "resources/infobar_update@2x.png",
     "resources/infobar_update@3x.png",
     "resources/infobar_warning.png",
     "resources/infobar_warning@2x.png",
     "resources/infobar_warning@3x.png",
   ]
   outputs = [
     "{{bundle_resources_dir}}/{{source_file_part}}",
   ]
 }