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 136 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());
 
+  // Find the top match before possibly applying demotions.
+  if (!matches_.empty())
+    std::partial_sort(matches_.begin(), matches_.begin() +  1, matches_.end(),
+                      &AutocompleteMatch::MoreRelevant);
+  // Don't demote the top match if applicable.
+  OmniboxFieldTrial::UndemotableTopMatchTypes undemotable_top_types =
+      OmniboxFieldTrial::GetUndemotableTopTypes(
+          input.current_page_classification());
+  const bool preserve_top_match = !matches_.empty() &&
+      (undemotable_top_types.count(matches_.begin()->type) != 0);
+
   // 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);
+  std::sort(matches_.begin() + (preserve_top_match ? 1 : 0), 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;
          it != matches_.end(); ++it) {
       if (it->allowed_to_be_default_match) {
         std::rotate(matches_.begin(), it, it + 1);
         break;
@@ skipping 138 matching lines @@
   alternate_nav_url_ = rhs.alternate_nav_url_;
 }
 
 void AutocompleteResult::AddMatch(
     AutocompleteInput::PageClassification page_classification,
     const AutocompleteMatch& match) {
   DCHECK(default_match_ != end());
   DCHECK_EQ(AutocompleteMatch::SanitizeString(match.contents), match.contents);
   DCHECK_EQ(AutocompleteMatch::SanitizeString(match.description),
             match.description);
+  // GetUndemotableTopTypes() is not used here because it's done in
+  // SortAndCull(), and we depend on SortAndCull() to be called afterwards.
   CompareWithDemoteByType comparing_object(page_classification);
   ACMatches::iterator insertion_point =
       std::upper_bound(begin(), end(), match, comparing_object);
   matches_difference_type default_offset = default_match_ - begin();
   if ((insertion_point - begin()) <= default_offset)
     ++default_offset;
   matches_.insert(insertion_point, match);
   default_match_ = begin() + default_offset;
 }
 
@@ skipping 33 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--;
     }
   }
 }