sync_unit_tests: add test for unknown field retention.

chrome/browser/sync/protocol/sync_proto.gyp

 # Copyright (c) 2010 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
       # Protobuf compiler / generate rule for sync.proto.  This is used by
       # test code in net, which is why it's isolated into its own .gyp file.
       'target_name': 'sync_proto',
       'type': 'none',
       'sources': [
         'sync.proto',
         'encryption.proto',
         'app_specifics.proto',
         'autofill_specifics.proto',
         'bookmark_specifics.proto',
         'extension_specifics.proto',
         'nigori_specifics.proto',
         'password_specifics.proto',
         'preference_specifics.proto',
         'session_specifics.proto',
+        'test.proto',
         'theme_specifics.proto',
         'typed_url_specifics.proto',
       ],
       'rules': [
         {
           'rule_name': 'genproto',
           'extension': 'proto',
           'inputs': [
             '<(PRODUCT_DIR)/<(EXECUTABLE_PREFIX)protoc<(EXECUTABLE_SUFFIX)',
           ],
@@ skipping 38 matching lines @@
       },
     },
   ],
 }
 
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