Refactoring gamepad polling to support dynamically added sources

content/content_browser.gypi

Index: content/content_browser.gypi
diff --git a/content/content_browser.gypi b/content/content_browser.gypi
index 16a8895d930c1c2cd2ae8b9d0e6708dc3e18188f..9425dcc917a0f0b6588de790062c4b33bd934568 100644
--- a/content/content_browser.gypi
+++ b/content/content_browser.gypi
@@ -743,8 +743,8 @@
       'browser/frame_host/render_widget_host_view_guest.cc',
       'browser/frame_host/render_widget_host_view_guest.h',
       'browser/gamepad/gamepad_consumer.h',
-      'browser/gamepad/gamepad_data_fetcher.h',
       'browser/gamepad/gamepad_data_fetcher.cc',
+      'browser/gamepad/gamepad_data_fetcher.h',
       'browser/gamepad/gamepad_platform_data_fetcher.h',
       'browser/gamepad/gamepad_platform_data_fetcher_android.cc',
       'browser/gamepad/gamepad_platform_data_fetcher_android.h',
@@ -765,7 +765,7 @@
       'browser/gamepad/gamepad_standard_mappings_win.cc',
       'browser/gamepad/raw_input_data_fetcher_win.cc',
       'browser/gamepad/raw_input_data_fetcher_win.h',
-      'browser/gamepad/xbox_data_fetcher_mac.cc',
+      'browser/gamepad/xbox_data_fetcher_mac.mm',
       'browser/gamepad/xbox_data_fetcher_mac.h',
       'browser/geofencing/geofencing_dispatcher_host.cc',
       'browser/geofencing/geofencing_dispatcher_host.h',
@@ -1837,11 +1837,6 @@
         'browser/file_descriptor_info_impl.h',
       ]
     }],
-    ['OS!="win" and OS!="mac" and OS!="android" and (OS!="linux" or use_udev==0)', {
-      'sources': [
-        'browser/gamepad/gamepad_platform_data_fetcher.cc',
-      ]
-    }],
     ['OS=="ios"', {
       'sources/': [
         # iOS only needs a small portion of content; exclude all the