Update some comments about variations headers API use.

chrome/browser/safe_browsing/srt_fetcher_win.cc

Index: chrome/browser/safe_browsing/srt_fetcher_win.cc
diff --git a/chrome/browser/safe_browsing/srt_fetcher_win.cc b/chrome/browser/safe_browsing/srt_fetcher_win.cc
index 5f176dd9af85608a1da656bbf3447e6cfe4036b9..06c6aef552c967ecf38c871754b65bac84e27ea2 100644
--- a/chrome/browser/safe_browsing/srt_fetcher_win.cc
+++ b/chrome/browser/safe_browsing/srt_fetcher_win.cc
@@ -632,8 +632,8 @@ class SRTFetcher : public net::URLFetcherDelegate {
     ProfileIOData* io_data = ProfileIOData::FromResourceContext(
         profile_->GetResourceContext());
     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(
         url_fetcher_->GetOriginalURL(), io_data->IsOffTheRecord(),