Convert //ios from scoped_ptr to std::unique_ptr.

ios/chrome/browser/signin/account_fetcher_service_factory.cc

Index: ios/chrome/browser/signin/account_fetcher_service_factory.cc
diff --git a/ios/chrome/browser/signin/account_fetcher_service_factory.cc b/ios/chrome/browser/signin/account_fetcher_service_factory.cc
index cce0abdcfb0cb87b670fd8380994f5c21791afed..f052d4f15c1e1dde32fb0b6c4c515d5991200ab1 100644
--- a/ios/chrome/browser/signin/account_fetcher_service_factory.cc
+++ b/ios/chrome/browser/signin/account_fetcher_service_factory.cc
@@ -45,11 +45,12 @@ void AccountFetcherServiceFactory::RegisterBrowserStatePrefs(
   AccountFetcherService::RegisterPrefs(registry);
 }
 
-scoped_ptr<KeyedService> AccountFetcherServiceFactory::BuildServiceInstanceFor(
+std::unique_ptr<KeyedService>
+AccountFetcherServiceFactory::BuildServiceInstanceFor(
     web::BrowserState* context) const {
   ios::ChromeBrowserState* browser_state =
       ios::ChromeBrowserState::FromBrowserState(context);
-  scoped_ptr<AccountFetcherService> service(new AccountFetcherService());
+  std::unique_ptr<AccountFetcherService> service(new AccountFetcherService());
   service->Initialize(
       SigninClientFactory::GetForBrowserState(browser_state),
       OAuth2TokenServiceFactory::GetForBrowserState(browser_state),