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

components/autofill/core/browser/autocomplete_history_manager.cc

Index: components/autofill/core/browser/autocomplete_history_manager.cc
diff --git a/components/autofill/core/browser/autocomplete_history_manager.cc b/components/autofill/core/browser/autocomplete_history_manager.cc
index 79d75b8c18d257b686c4121a9dbc5f7dedc8772a..8385d273c7bd7429777f9af1938957e18b991a72 100644
--- a/components/autofill/core/browser/autocomplete_history_manager.cc
+++ b/components/autofill/core/browser/autocomplete_history_manager.cc
@@ -9,12 +9,14 @@
 #include "base/prefs/pref_service.h"
 #include "base/profiler/scoped_tracker.h"
 #include "base/strings/string16.h"
+#include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "components/autofill/core/browser/autofill_client.h"
 #include "components/autofill/core/browser/autofill_driver.h"
 #include "components/autofill/core/browser/autofill_external_delegate.h"
 #include "components/autofill/core/browser/validation.h"
 #include "components/autofill/core/common/autofill_pref_names.h"
+#include "components/autofill/core/common/autofill_util.h"
 #include "components/autofill/core/common/form_data.h"
 
 namespace autofill {
@@ -81,7 +83,31 @@ void AutocompleteHistoryManager::OnWebDataServiceRequestDone(
   const WDResult<std::vector<base::string16> >* autofill_result =
       static_cast<const WDResult<std::vector<base::string16> >*>(result);
   std::vector<base::string16> suggestions = autofill_result->GetValue();
-  SendSuggestions(&suggestions);
+
+  if (!IsFeatureSubstringMatchEnabled() || user_input_.empty()) {
+    SendSuggestions(&suggestions);
+  } else {
+    std::vector<base::string16> prefix_suggestions;
+    std::vector<base::string16> substring_suggestions;
+    for (base::string16 suggestion : suggestions) {
+      // Populate all suggestions with prefix matched followed by substring
+      // matched.
+      if (StartsWith(suggestion, user_input_, false)) {
+        prefix_suggestions.push_back(suggestion);
+      } else if (IsContentsPrefixOfSuggestionToken(suggestion, user_input_,
+                                                   CASE_IGNORE)) {
+        substring_suggestions.push_back(suggestion);
+      }
+    }
+
+    // Now append substring matched suggestions to the prefix matched
+    // suggestion list.
+    for (base::string16 substring_match : substring_suggestions) {
+      prefix_suggestions.push_back(substring_match);
+    }
+
+    SendSuggestions(&prefix_suggestions);
+  }
 }
 
 void AutocompleteHistoryManager::OnGetAutocompleteSuggestions(
@@ -101,8 +127,10 @@ void AutocompleteHistoryManager::OnGetAutocompleteSuggestions(
   }
 
   if (database_.get()) {
+    user_input_ = prefix;
     pending_query_handle_ = database_->GetFormValuesForElementName(
-        name, prefix, kMaxAutocompleteMenuItems, this);
+        name, IsFeatureSubstringMatchEnabled() ? base::string16() : prefix,
+        kMaxAutocompleteMenuItems, this);
   }
 }