GCAPI should append to the existing experiment_labels instead of clobbering them.

chrome/chrome_common.gypi

 # Copyright (c) 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.
 
 {
   'targets': [
     {
       'target_name': 'common',
       'type': 'static_library',
       'variables': {
@@ skipping 320 matching lines @@
         'common/mac/objc_zombie.mm',
         'common/media/webrtc_logging_messages.h',
         'common/metrics/caching_permuted_entropy_provider.cc',
         'common/metrics/caching_permuted_entropy_provider.h',
         'common/metrics/metrics_log_base.cc',
         'common/metrics/metrics_log_base.h',
         'common/metrics/metrics_log_manager.cc',
         'common/metrics/metrics_log_manager.h',
         'common/metrics/metrics_service_base.cc',
         'common/metrics/metrics_service_base.h',
+        'common/metrics/variations/experiment_labels_win.cc',
+        'common/metrics/variations/experiment_labels_win.h',
         'common/metrics/variations/uniformity_field_trials.cc',
         'common/metrics/variations/uniformity_field_trials.h',
         'common/metrics/variations/variations_util.cc',
         'common/metrics/variations/variations_util.h',
         'common/multi_process_lock.h',
         'common/multi_process_lock_linux.cc',
         'common/multi_process_lock_mac.cc',
         'common/multi_process_lock_win.cc',
         'common/omaha_query_params/omaha_query_params.cc',
         'common/omaha_query_params/omaha_query_params.h',
@@ skipping 427 matching lines @@
         'common/metrics/proto/user_action_event.proto',
       ],
       'variables': {
         'proto_in_dir': 'common/metrics/proto',
         'proto_out_dir': 'chrome/common/metrics/proto',
       },
       'includes': [ '../build/protoc.gypi' ],
     },
   ],
 }