[ObjC ARC] Converts components/sessions:unit_tests to ARC.

components/sessions/BUILD.gn

 # Copyright 2014 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.
 
 if (is_android) {
   import("//build/config/android/config.gni")
 }
 
 config("implementation") {
   defines = [ "SESSIONS_IMPLEMENTATION" ]
@@ skipping 141 matching lines @@
 
   if (!is_android && !is_ios) {
     sources += [
       "core/base_session_service_test_helper.cc",
       "core/base_session_service_test_helper.h",
     ]
   }
 }
 
 source_set("unit_tests") {
+  if (is_ios) {
+    configs += [ "//build/config/compiler:enable_arc" ]

[Mr4D (OOO till 08-26), 2017/06/12 21:13:32]

I am confused now: Do we want to allow ARC for iOS? How does that work?

+  }
   testonly = true
   sources = [
     "core/serialized_navigation_entry_unittest.cc",
     "core/session_backend_unittest.cc",
     "core/session_types_unittest.cc",
     "ios/ios_serialized_navigation_builder_unittest.mm",

[stkhapugin, 2017/06/13 12:09:58]

Maybe we should move this test to a new target, unit_tests_ios or
ios:unit_tests, instead of conditional flag flipping? 

     "ios/ios_serialized_navigation_driver_unittest.cc",
   ]
 
   if (!is_ios) {
     sources += [
       "content/content_serialized_navigation_builder_unittest.cc",
       "content/content_serialized_navigation_driver_unittest.cc",
     ]
   }
 
   public_deps = [
     ":sessions",
   ]
 
   deps = [
     ":test_support",
     "//base/test:test_support",
     "//components/sync",
     "//testing/gtest",
     "//ui/base",  # For page transition types.
     "//url",
   ]
 
   if (!is_ios) {
     deps += [ "//content/public/common" ]
   }
 }