Update some comments about variations headers API use.

chrome/browser/safe_browsing/srt_fetcher_win.cc

 // Copyright 2015 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 "chrome/browser/safe_browsing/srt_fetcher_win.h"
 
 #include <stdint.h>
 
 #include <algorithm>
 #include <memory>
@@ skipping 614 matching lines @@
     url_fetcher_->SetLoadFlags(net::LOAD_DISABLE_CACHE);
     url_fetcher_->SetMaxRetriesOn5xx(3);
     url_fetcher_->SaveResponseToTemporaryFile(
         BrowserThread::GetTaskRunnerForThread(BrowserThread::FILE));
     url_fetcher_->SetRequestContext(
         g_browser_process->system_request_context());
     // Adds the UMA bit to the download request if the user is enrolled in UMA.
     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(),
         ChromeMetricsServiceAccessor::IsMetricsAndCrashReportingEnabled(),
         is_signed_in, &headers);
     url_fetcher_->SetExtraRequestHeaders(headers.ToString());
     url_fetcher_->Start();
   }
 
   // net::URLFetcherDelegate:
@@ skipping 451 matching lines @@
   return srt_cleaner_key.Open(HKEY_CURRENT_USER, cleaner_key_path.c_str(),
                               KEY_QUERY_VALUE) == ERROR_SUCCESS &&
          srt_cleaner_key.GetValueCount() > 0;
 }
 
 void SetSwReporterTestingDelegate(SwReporterTestingDelegate* delegate) {
   g_testing_delegate_ = delegate;
 }
 
 }  // namespace safe_browsing