AppShell: Enable chrome.fileSystem.retainEntry/restoreEntry

extensions/shell/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//build/util/process_version.gni")
 import("//extensions/features/features.gni")
 import("//testing/test.gni")
 import("//tools/grit/grit_rule.gni")
@@ skipping 170 matching lines @@
       "browser/shell_native_app_window_aura.h",
       "browser/shell_screen.cc",
       "browser/shell_screen.h",
     ]
     deps += [
       "//ui/wm",
       "//ui/wm/public",
     ]
   }
 
+  if (is_desktop_linux) {
+    sources += [
+      "browser/api/file_system/shell_file_system_delegate.cc",
+      "browser/api/file_system/shell_file_system_delegate.h",
+    ]
+  }
+
   if (is_chromeos) {
     sources += [
       "browser/api/vpn_provider/vpn_service_factory.cc",
       "browser/api/vpn_provider/vpn_service_factory.h",
     ]
     deps += [
       "//chromeos",
       "//ui/chromeos",
       "//ui/display/manager",
     ]
@@ skipping 249 matching lines @@
     "//extensions/browser",
   ]
 
   if (is_chromeos) {
     deps += [
       "//chromeos:test_support",
       "//components/keyed_service/content",
     ]
   }
 }