Set a zero suggest impression for most visited.

chrome/browser/autocomplete/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 "chrome/browser/autocomplete/zero_suggest_provider.h"
 
 #include "base/callback.h"
 #include "base/i18n/case_conversion.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/metrics/histogram.h"
@@ skipping 144 matching lines @@
   done_ = true;
 
   if (clear_cached_results) {
     // We do not call Clear() on |results_| to retain |verbatim_relevance|
     // value in the |results_| object. |verbatim_relevance| is used at the
     // beginning of the next OnOmniboxFocused() call to determine the current
     // url match relevance.
     results_.suggest_results.clear();
     results_.navigation_results.clear();
     current_query_.clear();
+    most_visited_urls_.clear();
   }
 }
 
 void ZeroSuggestProvider::DeleteMatch(const AutocompleteMatch& match) {
   if (OmniboxFieldTrial::InZeroSuggestPersonalizedFieldTrial()) {
     // Remove the deleted match from the cache, so it is not shown to the user
     // again. Since we cannot remove just one result, blow away the cache.
     profile_->GetPrefs()->SetString(prefs::kZeroSuggestCachedResults,
                                     std::string());
   }
   BaseSearchProvider::DeleteMatch(match);
 }
 
 void ZeroSuggestProvider::AddProviderInfo(ProvidersInfo* provider_info) const {
   BaseSearchProvider::AddProviderInfo(provider_info);
-  if (!results_.suggest_results.empty() || !results_.navigation_results.empty())
+  if (!results_.suggest_results.empty() ||
+      !results_.navigation_results.empty() ||
+      !most_visited_urls_.empty())
     provider_info->back().set_times_returned_results_in_session(1);
 }
 
 void ZeroSuggestProvider::ResetSession() {
   // The user has started editing in the omnibox, so leave
   // |field_trial_triggered_in_session_| unchanged and set
   // |field_trial_triggered_| to false since zero suggest is inactive now.
   field_trial_triggered_ = false;
 }
 
@@ skipping 292 matching lines @@
   if (!json_data.empty()) {
     scoped_ptr<base::Value> data(
         SearchSuggestionParser::DeserializeJsonData(json_data));
     if (data && ParseSuggestResults(
             *data, kDefaultZeroSuggestRelevance, false, &results_)) {
       ConvertResultsToAutocompleteMatches();
       results_from_cache_ = !matches_.empty();
     }
   }
 }