[ios] Removed CookieStoreIOS::set_flush_delay_for_testing.

ios/net/cookies/cookie_store_ios.mm

Index: ios/net/cookies/cookie_store_ios.mm
diff --git a/ios/net/cookies/cookie_store_ios.mm b/ios/net/cookies/cookie_store_ios.mm
index 149d22bd74089b3f6b8d13367f961bd77edf2710..ab44ece98428bf19ebad3772b89feb78aa44af50 100644
--- a/ios/net/cookies/cookie_store_ios.mm
+++ b/ios/net/cookies/cookie_store_ios.mm
@@ -705,7 +705,6 @@ CookieStoreIOS::CookieStoreIOS(
       system_store_(system_store),
       creation_time_manager_(new CookieCreationTimeManager),
       metrics_enabled_(false),
-      flush_delay_(base::TimeDelta::FromSeconds(10)),
       synchronization_state_(NOT_SYNCHRONIZED),
       cookie_cache_(new CookieCache()),
       weak_factory_(this) {
@@ -809,7 +808,7 @@ void CookieStoreIOS::OnSystemCookiesChanged() {
   flush_closure_.Reset(base::Bind(&CookieStoreIOS::FlushStore,
                                   weak_factory_.GetWeakPtr(), base::Closure()));
   base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
-      FROM_HERE, flush_closure_.callback(), flush_delay_);
+      FROM_HERE, flush_closure_.callback(), base::TimeDelta::FromSeconds(10));
 }
 
 std::unique_ptr<net::CookieStore::CookieChangedSubscription>