[Cronet] Don't spam log if system cookie doesn't have creation time.

ios/features.gni

Index: ios/features.gni
diff --git a/ios/features.gni b/ios/features.gni
new file mode 100644
index 0000000000000000000000000000000000000000..050b0f81c9d8713aec07987060354301249e6292
--- /dev/null
+++ b/ios/features.gni
@@ -0,0 +1,10 @@
+# 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.
+
+declare_args() {
+  # Control whether cronet is build (this is usually set by the script
+  # components/cronet/tools/cr_cronet.py as cronet requires specific
+  # gn args to build correctly).
+  is_cronet_build = false
+}