Add a comment and DCHECK to require |session_storage| to be non-nil in WebState::CreateWithStorageS…

ios/web/public/web_state/web_state.h

Index: ios/web/public/web_state/web_state.h
diff --git a/ios/web/public/web_state/web_state.h b/ios/web/public/web_state/web_state.h
index aa55ba6a7c3ff0fcbd02ab33307c47573bd7993b..90adba4dfb7d2dccae8a32f37da654352f7c92d7 100644
--- a/ios/web/public/web_state/web_state.h
+++ b/ios/web/public/web_state/web_state.h
@@ -93,7 +93,8 @@ class WebState : public base::SupportsUserData {
   // Creates a new WebState.
   static std::unique_ptr<WebState> Create(const CreateParams& params);
 
-  // Creates a new WebState from a serialized NavigationManager.
+  // Creates a new WebState from a serialized representation of the session.
+  // |session_storage| must not be nil.
   static std::unique_ptr<WebState> CreateWithStorageSession(
       const CreateParams& params,
       CRWSessionStorage* session_storage);