Don't demote top match for certain match types.

chrome/browser/autocomplete/autocomplete_result.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/autocomplete_result.h"
 
 #include <algorithm>
 #include <iterator>
 
 #include "base/logging.h"
@@ skipping 29 matching lines @@
 CompareWithDemoteByType::CompareWithDemoteByType(
     AutocompleteInput::PageClassification current_page_classification) {
   OmniboxFieldTrial::GetDemotionsByType(current_page_classification,
                                         &demotions_);
 }
 
 int CompareWithDemoteByType::GetDemotedRelevance(
     const AutocompleteMatch& match) {
   OmniboxFieldTrial::DemotionMultipliers::const_iterator demotion_it =
       demotions_.find(match.type);
-  return (demotion_it == demotions_.end()) ?
+  return (demotion_it == demotions_.end() || !match.demoteable) ?
       match.relevance : (match.relevance * demotion_it->second);
 }
 
 bool CompareWithDemoteByType::operator()(const AutocompleteMatch& elem1,
                                          const AutocompleteMatch& elem2) {
   // Compute demoted relevance scores for each match.
   const int demoted_relevance1 = GetDemotedRelevance(elem1);
   const int demoted_relevance2 = GetDemotedRelevance(elem2);
   // For equal-relevance matches, we sort alphabetically, so that providers
   // who return multiple elements at the same priority get a "stable" sort
@@ skipping 86 matching lines @@
   for (ACMatches::iterator i(matches_.begin()); i != matches_.end(); ++i)
     i->ComputeStrippedDestinationURL(profile);
 
   // Remove duplicates.
   std::sort(matches_.begin(), matches_.end(),
             &AutocompleteMatch::DestinationSortFunc);
   matches_.erase(std::unique(matches_.begin(), matches_.end(),
                              &AutocompleteMatch::DestinationsEqual),
                  matches_.end());
 
+  // Don't demote the top match if applicable.
+  OmniboxFieldTrial::UndemotableTopMatchTypes undemotable_top_types;
+  OmniboxFieldTrial::GetUndemotableTopTypes(input.current_page_classification(),
+                                            &undemotable_top_types);
+  if (!matches_.empty() &&
+      undemotable_top_types.find(matches_.begin()->type) !=
+      undemotable_top_types.end()) {
+    matches_.begin()->demoteable = false;

[Peter Kasting, 2013/10/31 23:27:59]

Is this basically only used by code called from the block below?

Because if so, rather than add a new member to AutocompleteMatch, perhaps we
could simply pull off the front match here, run the sort/demote on the rest, and
then put the front match back.

[H Fung, 2013/11/01 23:42:56]

Yes, thanks.  I've made the change.

+  }
+
   // Sort and trim to the most relevant kMaxMatches matches.
   size_t max_num_matches = std::min(kMaxMatches, matches_.size());
   CompareWithDemoteByType comparing_object(input.current_page_classification());
   std::sort(matches_.begin(), matches_.end(), comparing_object);
   if (!matches_.empty() && !matches_.begin()->allowed_to_be_default_match &&
       OmniboxFieldTrial::ReorderForLegalDefaultMatch(
           input.current_page_classification())) {
     // Top match is not allowed to be the default match.  Find the most
     // relevant legal match and shift it to the front.
     for (AutocompleteResult::iterator it = matches_.begin() + 1;
@@ skipping 195 matching lines @@
        i != old_matches.rend() && delta > 0; ++i) {
     if (!HasMatchByDestination(*i, new_matches)) {
       AutocompleteMatch match = *i;
       match.relevance = std::min(max_relevance, match.relevance);
       match.from_previous = true;
       AddMatch(page_classification, match);
       delta--;
     }
   }
 }