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

ios/chrome/browser/web/early_page_script_perftest.mm

Index: ios/chrome/browser/web/early_page_script_perftest.mm
diff --git a/ios/chrome/browser/web/early_page_script_perftest.mm b/ios/chrome/browser/web/early_page_script_perftest.mm
index 87cf2f1040b245054e3bac17bdb1a08f1f648aa6..7851e5497d08cd5e903add9f522bb3d265aec2e4 100644
--- a/ios/chrome/browser/web/early_page_script_perftest.mm
+++ b/ios/chrome/browser/web/early_page_script_perftest.mm
@@ -3,7 +3,6 @@
 // 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"
@@ -14,6 +13,10 @@
 #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.
@@ -21,7 +24,7 @@
 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.
@@ -32,7 +35,7 @@ void InjectEarlyScript() {
   // 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.