Create a new chrome/browser/apps folder and move PlatformAppService there.

chrome/chrome_browser_extensions.gypi

Index: chrome/chrome_browser_extensions.gypi
diff --git a/chrome/chrome_browser_extensions.gypi b/chrome/chrome_browser_extensions.gypi
index d330d2070378e4952c9b8de6c4d7b54354017f6e..583a011f62f3fb760771272afb7c1792942e3a8e 100644
--- a/chrome/chrome_browser_extensions.gypi
+++ b/chrome/chrome_browser_extensions.gypi
@@ -550,10 +550,6 @@
         'browser/extensions/permissions_updater.h',
         'browser/extensions/platform_app_launcher.cc',
         'browser/extensions/platform_app_launcher.h',
-        'browser/extensions/platform_app_service.cc',
-        'browser/extensions/platform_app_service.h',
-        'browser/extensions/platform_app_service_factory.cc',
-        'browser/extensions/platform_app_service_factory.h',
         'browser/extensions/process_map.cc',
         'browser/extensions/process_map.h',
         'browser/extensions/requirements_checker.cc',
@@ -644,6 +640,10 @@
         'browser/extensions/window_controller_list_observer.h',
         'browser/extensions/window_event_router.cc',
         'browser/extensions/window_event_router.h',
+        'browser/platform_apps/platform_app_service.cc',
+        'browser/platform_apps/platform_app_service.h',
+        'browser/platform_apps/platform_app_service_factory.cc',
+        'browser/platform_apps/platform_app_service_factory.h',
       ],
       'conditions': [
         ['chromeos==0', {