[sync] Add WalletMetadataSpecifics protobuf.

sync/protocol/autofill_specifics.proto

 // 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.
 //
 // Sync protocol datatype extension for autofill.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
@@ skipping 153 matching lines @@
 
   optional WalletInfoType type = 1;
 
   // This field exists if and only if the "type" field equals to
   // MASKED_CREDIT_CARD.
   optional WalletMaskedCreditCard masked_card = 2;
 
   // This field exists if and only if the "type" field equals to ADDRESS.
   optional WalletPostalAddress address = 3;
 }
+
+// Wallet card and address usage information that can be synced.
+message WalletMetadataSpecifics {
+  enum Type {
+    UNKNOWN = 0;
+    CARD = 1;
+    ADDRESS = 2;
+  }
+
+  // The type of the Wallet metadata.
+  optional Type type = 1;
+
+  // Unique ID string of the corresponding Wallet data.

[Nicolas Zea, 2015/05/20 21:41:45]

nit: Information about how it's generated?

[please use gerrit instead, 2015/05/20 23:37:39]

Done.

+  optional string id = 2;
+
+  // The number of times that this Wallet card or address was used.
+  optional int64 use_count = 3;
+
+  // The last use date of this Wallet card or address.
+  optional int64 use_date = 4;

[Nicolas Zea, 2015/05/20 21:41:45]

nit: What are the units for this? Milliseconds since windows epoch?

[please use gerrit instead, 2015/05/20 23:37:39]

Done.

[please use gerrit instead, 2015/05/20 23:39:12]

As documented here:
https://code.google.com/p/chromium/codesearch#chromium/src/base/time/time_pos...

+}