Restrict transmission of external exp ids to signed in users.

components/ntp_snippets/remote/ntp_snippets_fetcher.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/ntp_snippets/remote/ntp_snippets_fetcher.h"
 
 #include <cstdlib>
 
 #include "base/command_line.h"
 #include "base/files/file_path.h"
@@ skipping 508 matching lines @@
                              net::LOAD_DO_NOT_SAVE_COOKIES);
 
   data_use_measurement::DataUseUserData::AttachToFetcher(
       url_fetcher_.get(), data_use_measurement::DataUseUserData::NTP_SNIPPETS);
 
   HttpRequestHeaders headers;
   if (!auth_header.empty())
     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.
   VLOG(1) << "Sending a NTP snippets request to " << url << ":" << std::endl
           << headers.ToString() << std::endl
           << request;
   // Fetchers are sometimes cancelled because a network change was detected.
   url_fetcher_->SetAutomaticallyRetryOnNetworkChanges(3);
   // Try to make fetching the files bit more robust even with poor connection.
   url_fetcher_->SetMaxRetriesOn5xx(3);
@@ skipping 320 matching lines @@
           interactive_request);
     case UserClassifier::UserClass::ACTIVE_SUGGESTIONS_CONSUMER:
       return request_throttler_active_suggestions_consumer_
           .DemandQuotaForRequest(interactive_request);
   }
   NOTREACHED();
   return false;
 }
 
 }  // namespace ntp_snippets