[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 acfb47df60fbf963abdbc98e9dfc45dc3b891fc1..e72f24ace41e4f97d6d0b84c081b64ae322b9608 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 +83,21 @@ 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() || pending_query_prefix_.empty()) {
+    SendSuggestions(&suggestions);
+  } else {
+    std::vector<base::string16> preferred_suggestions;
+    for (base::string16 suggestion : suggestions) {
+      if (StartsWith(suggestion, pending_query_prefix_, false) ||
+          IsContentsPrefixOfSuggestionToken(suggestion, pending_query_prefix_,
+                                            false)) {
+        preferred_suggestions.push_back(suggestion);
+      }
+    }
+
+    SendSuggestions(&preferred_suggestions);
+  }
 }
 
 void AutocompleteHistoryManager::OnGetAutocompleteSuggestions(
@@ -101,8 +117,10 @@ void AutocompleteHistoryManager::OnGetAutocompleteSuggestions(
   }
 
   if (database_.get()) {
+    pending_query_prefix_ = prefix;
     pending_query_handle_ = database_->GetFormValuesForElementName(
-        name, prefix, kMaxAutocompleteMenuItems, this);
+        name, IsFeatureSubstringMatchEnabled() ? base::string16() : prefix,
+        kMaxAutocompleteMenuItems, this);
   }
 }