[ObjC ARC] Converts ios/chrome/browser/web:perf_tests to ARC.

ios/chrome/browser/web/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.
 
 import("//ios/web/js_compile.gni")
 
 source_set("web") {
   configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
     "dom_altering_lock.h",
@@ skipping 323 matching lines @@
     "//ui/base",
     "//url",
   ]
   libs = [
     "UIKit.framework",
     "XCTest.framework",
   ]
 }
 
 source_set("perf_tests") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true
   sources = [
     "early_page_script_perftest.mm",
   ]
   deps = [
     "//base",
     "//ios/chrome/test/base:perf_test_support",
     "//ios/web",
     "//ios/web:test_support",
   ]
   libs = [ "WebKit.framework" ]
 }