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 b2b1fabd289445b32df607f6def36b94b4597f5d..2fb01a5a17dab01a5916342ddf2c75df57602c00 100644
--- a/components/ntp_snippets/remote/ntp_snippets_fetcher.cc
+++ b/components/ntp_snippets/remote/ntp_snippets_fetcher.cc
@@ -526,10 +526,13 @@ void NTPSnippetsFetcher::FetchSnippetsImpl(const GURL& url,
     headers.SetHeader("Authorization", auth_header);
   headers.SetHeader("Content-Type", "application/json; charset=UTF-8");
   // Add X-Client-Data header with experiment IDs from field trials.
-  variations::AppendVariationHeaders(url,
+  // 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);
   url_fetcher_->SetExtraRequestHeaders(headers.ToString());
   url_fetcher_->SetUploadData("application/json", request);
   // Log the request for debugging network issues.