[ObjC ARC] Converts ios/chrome/common:unit_tests to ARC.

ios/chrome/common/BUILD.gn

 # Copyright 2015 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.
 
 import("//build/buildflag_header.gni")
 import("//build/config/ios/ios_sdk.gni")
 
 source_set("common") {
   sources = [
     "channel_info.h",
@@ skipping 11 matching lines @@
     "//components/version_info",
     "//ios/chrome/common/app_group:main_app",
     "//ios/chrome/common/physical_web",
     "//net",
     "//url",
   ]
 
   libs = [ "QuartzCore.framework" ]
 }
 
-source_set("unit_tests") {
+source_set("noarc_unit_tests") {

[sdefresne, 2017/02/10 15:36:36]

Can you add a comment there says that this test should not use ARC? And do we
want to keep such a test when we are 100% ARC?

[lody, 2017/02/13 10:25:38]

Done.

   testonly = true
   sources = [
     "block_unittest.mm",
+  ]
+  deps = [
+    ":common",
+    "//base",
+    "//testing/gtest",
+  ]
+}
+
+source_set("unit_tests") {
+  configs += [ "//build/config/compiler:enable_arc" ]
+  testonly = true
+  sources = [
     "ns_regular_expression_unittest.mm",
     "string_util_unittest.mm",
     "x_callback_url_unittest.cc",
   ]
   deps = [
     ":common",
     "//base",
     "//testing/gtest",
   ]
 }
 
 buildflag_header("ios_app_bundle_id_prefix_header") {
   header = "ios_app_bundle_id_prefix.h"
   flags = [ "IOS_APP_BUNDLE_ID_PREFIX=\"$ios_app_bundle_id_prefix\"" ]
 }