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

ios/chrome/browser/web/early_page_script_perftest.mm

 // 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.
 
 #include "base/mac/bundle_locations.h"
-#include "base/mac/scoped_nsobject.h"
 #include "base/timer/elapsed_timer.h"
 #include "ios/chrome/test/base/perf_test_ios.h"
 #include "ios/web/public/test/fakes/test_browser_state.h"
 #import "ios/web/public/test/js_test_util.h"
 #import "ios/web/public/web_view_creation_util.h"
 #import "ios/web/web_state/js/page_script_util.h"
 
 #import <Foundation/Foundation.h>
 #import <WebKit/WebKit.h>
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 // Class for testing early page script injection into WKWebView.
 // TODO(crbug.com/583218): improve this test to use WKUserScript injections.
 class EarlyPageScriptPerfTest : public PerfTest {
  protected:
   EarlyPageScriptPerfTest() : PerfTest("Early Page Script for WKWebView") {
-    web_view_.reset([web::BuildWKWebView(CGRectZero, &browser_state_) retain]);
+    web_view_ = web::BuildWKWebView(CGRectZero, &browser_state_);
   }
 
   // Injects early script into WKWebView.
   void InjectEarlyScript() {
     web::ExecuteJavaScript(web_view_, web::GetEarlyPageScript(&browser_state_));
   }
 
   // BrowserState required for web view creation.
   web::TestBrowserState browser_state_;
   // WKWebView to test scripts injections.
-  base::scoped_nsobject<WKWebView> web_view_;
+  WKWebView* web_view_;
 };
 
 // Tests script loading time.
 TEST_F(EarlyPageScriptPerfTest, ScriptLoading) {
   RepeatTimedRuns("Loading",
                   ^base::TimeDelta(int) {
                     base::ElapsedTimer timer;
                     web::GetEarlyPageScript(&browser_state_);
                     return timer.Elapsed();
                   },
                   nil);
 }
 
 // Tests injection time into a bare web view.
 TEST_F(EarlyPageScriptPerfTest, BareWebViewInjection) {
   RepeatTimedRuns("Bare web view injection",
                   ^base::TimeDelta(int) {
                     base::ElapsedTimer timer;
                     InjectEarlyScript();
                     return timer.Elapsed();
                   },
                   nil);
 }
 
 }  // namespace