Observe input metrics from web content area.

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 1370 matching lines @@
       'browser/memory/oom_memory_details.cc',
       'browser/memory/oom_memory_details.h',
       'browser/memory/tab_manager.cc',
       'browser/memory/tab_manager.h',
       'browser/memory/tab_manager_delegate_chromeos.cc',
       'browser/memory/tab_manager_delegate_chromeos.h',
       'browser/memory/tab_manager_web_contents_data.cc',
       'browser/memory/tab_manager_web_contents_data.h',
       'browser/memory/tab_stats.cc',
       'browser/memory/tab_stats.h',
+      'browser/metrics/chrome_visibility_observer.cc',
+      'browser/metrics/chrome_visibility_observer.h',
+      'browser/metrics/desktop_engagement_observer.cc',
+      'browser/metrics/desktop_engagement_observer.h',
+      'browser/metrics/desktop_engagement_service.cc',
+      'browser/metrics/desktop_engagement_service.h',
       'browser/metrics/first_web_contents_profiler.cc',
       'browser/metrics/first_web_contents_profiler.h',
       'browser/net/firefox_proxy_settings.cc',
       'browser/net/firefox_proxy_settings.h',
       'browser/net/utility_process_mojo_proxy_resolver_factory.cc',
       'browser/net/utility_process_mojo_proxy_resolver_factory.h',
       'browser/obsolete_system/obsolete_system.h',
       'browser/obsolete_system/obsolete_system_linux.cc',
       'browser/obsolete_system/obsolete_system_mac.cc',
       'browser/obsolete_system/obsolete_system_win.cc',
@@ skipping 2900 matching lines @@
             '../components/components.gyp:rlz',
             '../components/components.gyp:search_engines',
             '../rlz/rlz.gyp:rlz_lib',
             'common',
           ],
         },
       ],
     }],
   ],
 }