Update some comments about variations headers API use.

components/omnibox/browser/zero_suggest_provider.cc

 // Copyright (c) 2012 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/omnibox/browser/zero_suggest_provider.h"
 
 #include <stddef.h>
 
 #include "base/callback.h"
 #include "base/i18n/case_conversion.h"
@@ skipping 315 matching lines @@
   } else {
     const int kFetcherID = 1;
     fetcher_ = net::URLFetcher::Create(kFetcherID, suggest_url,
                                        net::URLFetcher::GET, this);
     data_use_measurement::DataUseUserData::AttachToFetcher(
         fetcher_.get(), data_use_measurement::DataUseUserData::OMNIBOX);
     fetcher_->SetRequestContext(client()->GetRequestContext());
     fetcher_->SetLoadFlags(net::LOAD_DO_NOT_SAVE_COOKIES);
     // Add Chrome experiment state to the request headers.
     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(fetcher_->GetOriginalURL(),
                                        client()->IsOffTheRecord(), false,
                                        is_signed_in, &headers);
     fetcher_->SetExtraRequestHeaders(headers.ToString());
     fetcher_->Start();
     LogOmniboxZeroSuggestRequest(ZERO_SUGGEST_REQUEST_SENT);
   }
 }
 
@@ skipping 126 matching lines @@
   if (!json_data.empty()) {
     std::unique_ptr<base::Value> data(
         SearchSuggestionParser::DeserializeJsonData(json_data));
     if (data && ParseSuggestResults(
             *data, kDefaultZeroSuggestRelevance, false, &results_)) {
       ConvertResultsToAutocompleteMatches();
       results_from_cache_ = !matches_.empty();
     }
   }
 }