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

components/autofill/content/renderer/password_autofill_agent.cc

Index: components/autofill/content/renderer/password_autofill_agent.cc
diff --git a/components/autofill/content/renderer/password_autofill_agent.cc b/components/autofill/content/renderer/password_autofill_agent.cc
index 9999d26e2c38dbc120a14996b5593fa49264096f..0234b8daa9918bbef8298db0c25c020238941426 100644
--- a/components/autofill/content/renderer/password_autofill_agent.cc
+++ b/components/autofill/content/renderer/password_autofill_agent.cc
@@ -18,6 +18,7 @@
 #include "components/autofill/content/renderer/renderer_save_password_progress_logger.h"
 #include "components/autofill/core/common/autofill_constants.h"
 #include "components/autofill/core/common/autofill_switches.h"
+#include "components/autofill/core/common/autofill_util.h"
 #include "components/autofill/core/common/form_field_data.h"
 #include "components/autofill/core/common/password_form.h"
 #include "components/autofill/core/common/password_form_fill_data.h"
@@ -226,7 +227,8 @@ bool DoUsernamesMatch(const base::string16& username1,
                       bool exact_match) {
   if (exact_match)
     return username1 == username2;
-  return base::StartsWith(username1, username2, base::CompareCase::SENSITIVE);
+  return base::StartsWith(username1, username2, base::CompareCase::SENSITIVE) ||
+         ContainsTokenThatStartsWith(username1, username2, true);
 }
 
 // Returns |true| if the given element is editable. Otherwise, returns |false|.
@@ -421,11 +423,8 @@ bool FillUserNameAndPassword(
     username_element->setValue(username, true);
     nonscript_modified_values[*username_element] = username;
     username_element->setAutofilled(true);
-
-    if (set_selection) {
-      username_element->setSelectionRange(current_username.length(),
-                                          username.length());
-    }
+    if (set_selection)
+      PreviewSuggestion(username, current_username, username_element);
   } else if (current_username != username) {
     // If the username can't be filled and it doesn't match a saved password
     // as is, don't autofill a password.
@@ -803,10 +802,8 @@ bool PasswordAutofillAgent::PreviewSuggestion(
   username_selection_start_ = username_element.selectionStart();
   username_element.setSuggestedValue(username);
   username_element.setAutofilled(true);
-  username_element.setSelectionRange(
-      username_selection_start_,
-      username_element.suggestedValue().length());
-
+  ::autofill::PreviewSuggestion(username_element.suggestedValue(),
+                                username_element.value(), &username_element);
   was_password_autofilled_ = password_info->password_field.isAutofilled();
   password_info->password_field.setSuggestedValue(password);
   password_info->password_field.setAutofilled(true);