Add metrics for the number of attached displays.

chrome/chrome_browser.gypi

 # Copyright 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.
 
 {
   'variables': {
     # All .cc, .h, .m, and .mm files under browser except for:
     # * tests and mocks.
     # * code below browser/chromeos
     # * code below browser/extensions
@@ skipping 641 matching lines @@
       'browser/media/webrtc_log_list.cc',
       'browser/media/webrtc_log_list.h',
       'browser/memory_details.cc',
       'browser/memory_details.h',
       'browser/memory_details_android.cc',
       'browser/memory_details_linux.cc',
       'browser/memory_details_mac.cc',
       'browser/memory_details_win.cc',
       'browser/metrics/chrome_browser_main_extra_parts_metrics.cc',
       'browser/metrics/chrome_browser_main_extra_parts_metrics.h',
+      'browser/metrics/chrome_browser_main_extra_parts_metrics_mac.h',
+      'browser/metrics/chrome_browser_main_extra_parts_metrics_mac.mm',
       'browser/metrics/chrome_metrics_service_accessor.cc',
       'browser/metrics/chrome_metrics_service_accessor.h',
       'browser/metrics/chrome_metrics_service_client.cc',
       'browser/metrics/chrome_metrics_service_client.h',
       'browser/metrics/chrome_stability_metrics_provider.cc',
       'browser/metrics/chrome_stability_metrics_provider.h',
       'browser/metrics/field_trial_synchronizer.cc',
       'browser/metrics/field_trial_synchronizer.h',
       'browser/metrics/google_update_metrics_provider_win.cc',
       'browser/metrics/google_update_metrics_provider_win.h',
@@ skipping 2922 matching lines @@
           'variables': {
             'proto_in_dir': 'browser/sync_file_system/drive_backend',
             'proto_out_dir': 'chrome/browser/sync_file_system/drive_backend',
           },
           'includes': [ '../build/protoc.gypi' ]
         },
       ],
     },],
   ],
 }