[Autofill/Autocomplete Feature] Substring matching instead of prefix matching.

components/autofill/core/browser/autocomplete_history_manager.cc

 // Copyright 2013 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/autofill/core/browser/autocomplete_history_manager.h"
 
 #include <vector>
 
 #include "base/prefs/pref_service.h"
 #include "base/profiler/scoped_tracker.h"
@@ skipping 85 matching lines @@
   query_id_ = query_id;
   autofill_suggestions_ = suggestions;
   if (!autofill_client_->IsAutocompleteEnabled() ||
       form_control_type == "textarea" ||
       IsInAutofillSuggestionsDisabledExperiment()) {
     SendSuggestions(NULL);
     return;
   }
 
   if (database_.get()) {
+    pending_query_prefix_ = prefix;
     pending_query_handle_ = database_->GetFormValuesForElementName(
         name, prefix, kMaxAutocompleteMenuItems, this);
   }
 }
 
 void AutocompleteHistoryManager::OnFormSubmitted(const FormData& form) {
   if (!autofill_client_->IsAutocompleteEnabled())
     return;
 
   if (driver_->IsOffTheRecord())
@@ skipping 52 matching lines @@
     for (const auto& new_result : *autocomplete_results) {
       bool unique = true;
       for (const auto& autofill_suggestion : autofill_suggestions_) {
         // Don't add duplicate values.
         if (new_result == autofill_suggestion.value) {
           unique = false;
           break;
         }
       }
 
-      if (unique)
-        autofill_suggestions_.push_back(Suggestion(new_result));
+      if (unique) {
+        Suggestion s(new_result);
+        s.match_start = pending_query_prefix_.size();
+        autofill_suggestions_.push_back(s);
+      }
     }
   }
 
   external_delegate_->OnSuggestionsReturned(query_id_, autofill_suggestions_);
 
   query_id_ = 0;
   autofill_suggestions_.clear();
 }
 
 }  // namespace autofill