Converts parts of ios/web to ARC

ios/web/navigation/navigation_manager_impl.mm

Index: ios/web/navigation/navigation_manager_impl.mm
diff --git a/ios/web/navigation/navigation_manager_impl.mm b/ios/web/navigation/navigation_manager_impl.mm
index 3863404b8b43a92b64b975ab02d87b7de22679b2..fa78e2c8807e19e8357b8a6a27f2847f11eaa8e1 100644
--- a/ios/web/navigation/navigation_manager_impl.mm
+++ b/ios/web/navigation/navigation_manager_impl.mm
@@ -84,7 +84,7 @@ NavigationManagerImpl::~NavigationManagerImpl() {
 
 void NavigationManagerImpl::SetSessionController(
     CRWSessionController* session_controller) {
-  session_controller_.reset([session_controller retain]);
+  session_controller_.reset(session_controller);
   [session_controller_ setNavigationManager:this];
 }
 
@@ -92,21 +92,21 @@ void NavigationManagerImpl::InitializeSession(NSString* window_name,
                                               NSString* opener_id,
                                               BOOL opened_by_dom,
                                               int opener_navigation_index) {
-  SetSessionController([[[CRWSessionController alloc]
+  SetSessionController([[CRWSessionController alloc]
          initWithWindowName:window_name
                    openerId:opener_id
                 openedByDOM:opened_by_dom
       openerNavigationIndex:opener_navigation_index
-               browserState:browser_state_] autorelease]);
+               browserState:browser_state_]);
 }
 
 void NavigationManagerImpl::ReplaceSessionHistory(
     ScopedVector<web::NavigationItem> items,
     int current_index) {
-  SetSessionController([[[CRWSessionController alloc]
+  SetSessionController([[CRWSessionController alloc]
       initWithNavigationItems:std::move(items)
                  currentIndex:current_index
-                 browserState:browser_state_] autorelease]);
+                 browserState:browser_state_]);
 }
 
 void NavigationManagerImpl::SetFacadeDelegate(
@@ -322,8 +322,7 @@ void NavigationManagerImpl::RemoveTransientURLRewriters() {
 
 void NavigationManagerImpl::CopyState(
     NavigationManagerImpl* navigation_manager) {
-  SetSessionController(
-      [[navigation_manager->GetSessionController() copy] autorelease]);
+  SetSessionController([navigation_manager->GetSessionController() copy]);
 }
 
 }  // namespace web