Update some comments about variations headers API use.

ios/chrome/browser/ui/contextual_search/contextual_search_delegate.cc

Index: ios/chrome/browser/ui/contextual_search/contextual_search_delegate.cc
diff --git a/ios/chrome/browser/ui/contextual_search/contextual_search_delegate.cc b/ios/chrome/browser/ui/contextual_search/contextual_search_delegate.cc
index 3acaf6243c6bcf438fdbfdfa8efe1a4fa0fb8e00..47324cde34374be509a825c20e572bfd47d9e594 100644
--- a/ios/chrome/browser/ui/contextual_search/contextual_search_delegate.cc
+++ b/ios/chrome/browser/ui/contextual_search/contextual_search_delegate.cc
@@ -173,8 +173,8 @@ void ContextualSearchDelegate::RequestServerSearchTerm() {
 
   // Add Chrome experiment state to the request headers.
   net::HttpRequestHeaders headers;
-  // Note: It's fine to pass in |is_signed_in| false, which does not affect
-  // transmission of experiment ids coming from the variations server.
+  // Note: It's OK to pass |is_signed_in| false if it's unknown, as it does
+  // not affect transmission of experiments coming from the variations server.
   bool is_signed_in = false;
   variations::AppendVariationHeaders(search_term_fetcher_->GetOriginalURL(),
                                      browser_state_->IsOffTheRecord(), false,