Restrict transmission of external exp ids to signed in users.

components/ntp_snippets/remote/ntp_snippets_fetcher.cc

Index: components/ntp_snippets/remote/ntp_snippets_fetcher.cc
diff --git a/components/ntp_snippets/remote/ntp_snippets_fetcher.cc b/components/ntp_snippets/remote/ntp_snippets_fetcher.cc
index 62236a8a375cab50981b1a7798b0ce55f963798c..9bf1edf8e2a8b865cf61cbfa120b8c678dc63aac 100644
--- a/components/ntp_snippets/remote/ntp_snippets_fetcher.cc
+++ b/components/ntp_snippets/remote/ntp_snippets_fetcher.cc
@@ -678,10 +678,13 @@ std::string NTPSnippetsFetcher::RequestBuilder::BuildHeaders() const {
     headers.SetHeader("Authorization", auth_header_);
   }
   // Add X-Client-Data header with experiment IDs from field trials.
+  // Note: It's fine to pass in |is_signed_in| false, which does not affect
+  // transmission of experiment ids coming from the variations server.
+  bool is_signed_in = false;
   variations::AppendVariationHeaders(url_,
                                      false,  // incognito
                                      false,  // uma_enabled
-                                     &headers);
+                                     is_signed_in, &headers);
   return headers.ToString();
 }