Trying changes to see the perfomance impact on Mac....

chrome/chrome_browser.gypi

 # Copyright (c) 2011 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': 'browser',
       'type': '<(library)',
       'msvs_guid': '5BF908A7-68FB-4A4B-99E3-8C749F1FE4EA',
@@ skipping 1338 matching lines @@
         'browser/memory_purger.h',
         'browser/metrics/histogram_synchronizer.cc',
         'browser/metrics/histogram_synchronizer.h',
         'browser/metrics/metric_event_duration_details.h',
         'browser/metrics/metrics_log.cc',
         'browser/metrics/metrics_log.h',
         'browser/metrics/metrics_response.cc',
         'browser/metrics/metrics_response.h',
         'browser/metrics/metrics_service.cc',
         'browser/metrics/metrics_service.h',
+        'browser/metrics/thread_watcher.cc',
+        'browser/metrics/thread_watcher.h',
         'browser/metrics/user_metrics.cc',
         'browser/metrics/user_metrics.h',
         'browser/nacl_host/nacl_broker_host_win.cc',
         'browser/nacl_host/nacl_broker_host_win.h',
         'browser/nacl_host/nacl_broker_service_win.cc',
         'browser/nacl_host/nacl_broker_service_win.h',
         'browser/nacl_host/nacl_process_host.cc',
         'browser/nacl_host/nacl_process_host.h',
         'browser/net/blob_url_request_job_factory.cc',
         'browser/net/blob_url_request_job_factory.h',
@@ skipping 3114 matching lines @@
       ],
     },
   ],
 }
 
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