[Autofill] Update the autocomplete types implementation to match the current HTML spec.

chrome/browser/autofill/autofill_field.cc

 // Copyright (c) 2011 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 "chrome/browser/autofill/autofill_field.h"
 
 #include "base/logging.h"
 #include "base/sha1.h"
 #include "base/string_number_conversions.h"
 #include "base/utf_string_conversions.h"
@@ skipping 56 matching lines @@
 
   return heuristic_type_;
 }
 
 bool AutofillField::IsEmpty() const {
   return value.empty();
 }
 
 std::string AutofillField::FieldSignature() const {
   std::string field_name = UTF16ToUTF8(name);
-  std::string type = UTF16ToUTF8(form_control_type);
-  std::string field_string = field_name + "&" + type;
+  std::string field_string = field_name + "&" + form_control_type;
   return Hash32Bit(field_string);
 }
 
 bool AutofillField::IsFieldFillable() const {
   return type() != UNKNOWN_TYPE;
 }