[ObjC ARC] Converts ios/web:ios_web_general_unittests to ARC.

ios/web/test/web_test_unittest.mm

 // Copyright 2017 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 <WebKit/WebKit.h>
 
 #import "ios/web/public/test/fakes/test_web_view_content_view.h"
 #import "ios/web/test/web_test_with_web_controller.h"
 #import "ios/web/test/wk_web_view_crash_utils.h"
 #include "testing/gtest/include/gtest/gtest-spi.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 // Fixture to test that the WebTest fixture properly fails tests when the render
 // process crashes.
 class WebTestFixtureTest : public web::WebTestWithWebController {
  protected:
   void SetUp() override {
     web::WebTestWithWebController::SetUp();
-    web_view_.reset([web::BuildTerminatedWKWebView() retain]);
-    base::scoped_nsobject<TestWebViewContentView> web_view_content_view(
+    web_view_ = web::BuildTerminatedWKWebView();
+    TestWebViewContentView* web_view_content_view =
         [[TestWebViewContentView alloc]
             initWithMockWebView:web_view_
-                     scrollView:[web_view_ scrollView]]);
+                     scrollView:[web_view_ scrollView]];
     [web_controller() injectWebViewContentView:web_view_content_view];
   }
 
-  base::scoped_nsobject<WKWebView> web_view_;
+  WKWebView* web_view_;
 };
 
 // Tests that the WebTest fixture triggers a test failure when a render process
 // crashes during the test.
 TEST_F(WebTestFixtureTest, FailsOnRenderCrash) {
   // EXPECT_FATAL_FAILURE() uses a local class, which cannot access non-static
   // variables of the enclosing function.
   static WKWebView* web_view = web_view_;
 
   EXPECT_FATAL_FAILURE(web::SimulateWKWebViewCrash(web_view),
                        "Renderer process died unexpectedly");
 };
 
 // Tests that |SetIgnoreRenderProcessCrashesDuringTesting()| properly ignores
 // intentional render process crashes.
 TEST_F(WebTestFixtureTest, SucceedsOnRenderCrash) {
   SetIgnoreRenderProcessCrashesDuringTesting(true);
   web::SimulateWKWebViewCrash(web_view_);
 };
 
 }  // namespace