Don't ever attempt to upload credit cards whose numbers match.

components/autofill/core/browser/credit_card.h

 // 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.
 
 #ifndef COMPONENTS_AUTOFILL_CORE_BROWSER_CREDIT_CARD_H_
 #define COMPONENTS_AUTOFILL_CORE_BROWSER_CREDIT_CARD_H_
 
 #include <iosfwd>
 #include <string>
 #include <utility>
@@ skipping 134 matching lines @@
   // or < 0, or > 0 if it is different.  The implied ordering can be used for
   // culling duplicates.  The ordering is based on collation order of the
   // textual contents of the fields.
   // GUIDs, origins, labels, and unique IDs are not compared, only the values of
   // the credit cards themselves.
   int Compare(const CreditCard& credit_card) const;
 
   // Determines if |this| is a local version of the server card |other|.
   bool IsLocalDuplicateOfServerCard(const CreditCard& other) const;
 
+  // Determines if |this| has the same number as |other|. If either is a masked
+  // server card, compares the last four digits only.
+  bool HasSameNumberAs(const CreditCard& other) const;
+
   // Equality operators compare GUIDs, origins, and the contents.
   // Usage metadata (use count, use date, modification date) are NOT compared.
   bool operator==(const CreditCard& credit_card) const;
   bool operator!=(const CreditCard& credit_card) const;
 
   // How this card is stored.
   RecordType record_type() const { return record_type_; }
   void set_record_type(RecordType rt) { record_type_ = rt; }
 
   // Returns true if there are no values (field types) set.
@@ skipping 81 matching lines @@
 extern const char kDiscoverCard[];
 extern const char kGenericCard[];
 extern const char kJCBCard[];
 extern const char kMasterCard[];
 extern const char kUnionPay[];
 extern const char kVisaCard[];
 
 }  // namespace autofill
 
 #endif  // COMPONENTS_AUTOFILL_CORE_BROWSER_CREDIT_CARD_H_