Add UMA stat to track home button and page prefs

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.
 
 {
   'targets': [
     {
       'target_name': 'browser',
       'type': 'static_library',
       'variables': { 'enable_wexit_time_destructors': 1, },
@@ skipping 1434 matching lines @@
         'browser/prefs/browser_prefs.cc',
         'browser/prefs/browser_prefs.h',
         'browser/prefs/chrome_pref_service_factory.cc',
         'browser/prefs/chrome_pref_service_factory.h',
         'browser/prefs/command_line_pref_store.cc',
         'browser/prefs/command_line_pref_store.h',
         'browser/prefs/incognito_mode_prefs.cc',
         'browser/prefs/incognito_mode_prefs.h',
         'browser/prefs/pref_model_associator.cc',
         'browser/prefs/pref_model_associator.h',
+        'browser/prefs/pref_metrics_service.cc',
+        'browser/prefs/pref_metrics_service.h',
         'browser/prefs/pref_service_syncable.cc',
         'browser/prefs/pref_service_syncable.h',
         'browser/prefs/pref_service_syncable_builder.cc',
         'browser/prefs/pref_service_syncable_builder.h',
         'browser/prefs/pref_service_syncable_observer.h',
         'browser/prefs/proxy_config_dictionary.cc',
         'browser/prefs/proxy_config_dictionary.h',
         'browser/prefs/proxy_prefs.cc',
         'browser/prefs/proxy_prefs.h',
         'browser/prefs/scoped_user_pref_update.cc',
@@ skipping 1881 matching lines @@
             'package_name': 'org/chromium/chrome/browser/ui/toolbar',
             'template_deps': ['browser/ui/toolbar/toolbar_model_security_level_list.h'],
           },
           'includes': [ '../build/android/java_cpp_template.gypi' ],
         },
       ],
      },
     ],
   ],
 }