Teach PasswordAutofillAgent sometimes match prefixes of usernames

chrome/renderer/autofill/password_autofill_agent_browsertest.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 "components/autofill/content/renderer/password_autofill_agent.h"
 
 #include "base/macros.h"
 #include "base/run_loop.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
@@ skipping 676 matching lines @@
        AutocompletePasswordForReadonlyUsernameMatched) {
   username_element_.SetValue(WebString::FromUTF16(username3_));
   SetElementReadOnly(username_element_, true);
 
   // Filled even though username is not the preferred match.
   SimulateOnFillPasswordForm(fill_data_);
   CheckTextFieldsState(UTF16ToUTF8(username3_), false,
                        UTF16ToUTF8(password3_), true);
 }
 
+// Fill a password field if the stored username is a prefix of username in
+// read-only field.
+TEST_F(PasswordAutofillAgentTest,
+       AutocompletePasswordForReadonlyUsernamePrefixMatched) {
+  base::string16 username_at = username3_ + base::UTF8ToUTF16("@example.com");
+  username_element_.SetValue(WebString::FromUTF16(username3_));
+  SetElementReadOnly(username_element_, true);
+
+  // Filled even though username is not the preferred match.
+  SimulateOnFillPasswordForm(fill_data_);
+  CheckTextFieldsState(UTF16ToUTF8(username3_), false, UTF16ToUTF8(password3_),
+                       true);
+}
 // If a username field is empty and readonly, don't autofill.
 TEST_F(PasswordAutofillAgentTest,
        NoAutocompletePasswordForReadonlyUsernameUnmatched) {
   username_element_.SetValue(WebString::FromUTF8(""));
   SetElementReadOnly(username_element_, true);
 
   SimulateOnFillPasswordForm(fill_data_);
   CheckTextFieldsState(std::string(), false, std::string(), false);
 }
 
@@ skipping 2212 matching lines @@
 TEST_F(PasswordAutofillAgentTest, AutocompleteWhenPageUrlIsChanged) {
   // Simulate that JavaScript changes url.
   fill_data_.origin = GURL(fill_data_.origin.possibly_invalid_spec() + "/path");
 
   SimulateOnFillPasswordForm(fill_data_);
 
   // The username and password should have been autocompleted.
   CheckTextFieldsState(kAliceUsername, true, kAlicePassword, true);
 }
 }  // namespace autofill