[Autofill] Correctly fill month selects where the first value is negative.

components/autofill/core/browser/autofill_field.cc

 // Copyright 2013 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/core/browser/autofill_field.h"
 
 #include <stdint.h>
 
 #include "base/command_line.h"
 #include "base/i18n/string_search.h"
@@ skipping 196 matching lines @@
   if (trimmed_values.size() == 12) {
     // The select presumable only contains the year's months.
     // If the first value of the select is 0, decrement the value of |month| so
     // January is associated with 0 instead of 1.
     int first_value;
     if (StringToInt(trimmed_values[0], &first_value) && first_value == 0)
       --month;
   } else if (trimmed_values.size() == 13) {
     // The select presumably uses the first value as a placeholder.
     int first_value;
-    // If the first value is not a number. Check the second value and apply the
-    // same logic as if there was no placeholder.
-    if (!StringToInt(trimmed_values[0], &first_value)) {
+    // If the first value is not a number or is a negative one, check the second
+    // value and apply the same logic as if there was no placeholder.
+    if (!StringToInt(trimmed_values[0], &first_value) || first_value < 0) {
       int second_value;
       if (StringToInt(trimmed_values[1], &second_value) && second_value == 0)
         --month;
     } else if (first_value == 1) {
       // If the first value of the select is 1, increment the value of |month|
       // to skip the placeholder value (January = 2).
       ++month;
     }
   }
 
@@ skipping 415 matching lines @@
   }
   return best_match;
 }
 
 bool AutofillField::IsCreditCardPrediction() const {
   return AutofillType(server_type_).group() == CREDIT_CARD ||
          AutofillType(heuristic_type_).group() == CREDIT_CARD;
 }
 
 }  // namespace autofill