[ObjC ARC] Converts ios/web/public/test:test to ARC.

ios/web/public/test/web_test.mm

 // 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.
 
 #include "ios/web/public/test/web_test.h"
 
 #include "base/memory/ptr_util.h"
 #include "ios/web/public/active_state_manager.h"
 #include "ios/web/public/web_state/global_web_state_observer.h"
 #import "ios/web/public/test/fakes/test_web_client.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace web {
 
 class WebTestRenderProcessCrashObserver : public GlobalWebStateObserver {
  public:
   WebTestRenderProcessCrashObserver() = default;
   ~WebTestRenderProcessCrashObserver() override = default;
 
   void RenderProcessGone(WebState* web_state) override {
     FAIL() << "Renderer process died unexpectedly during the test";
   }
@@ skipping 25 matching lines @@
 
 void WebTest::SetIgnoreRenderProcessCrashesDuringTesting(bool allow) {
   if (allow) {
     crash_observer_ = nullptr;
   } else {
     crash_observer_ = base::MakeUnique<WebTestRenderProcessCrashObserver>();
   }
 }
 
 }  // namespace web