Move fileSystem API FilePicker class to own file

chrome/browser/extensions/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("//chrome/common/features.gni")
 import("//extensions/features/features.gni")
 import("//media/media_options.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
@@ skipping 174 matching lines @@
     "api/extension_action/extension_action_api.cc",
     "api/extension_action/extension_action_api.h",
     "api/extension_action/extension_page_actions_api_constants.cc",
     "api/extension_action/extension_page_actions_api_constants.h",
     "api/feedback_private/feedback_private_api.cc",
     "api/feedback_private/feedback_private_api.h",
     "api/feedback_private/feedback_service.cc",
     "api/feedback_private/feedback_service.h",
     "api/file_handlers/non_native_file_system_delegate_chromeos.cc",
     "api/file_handlers/non_native_file_system_delegate_chromeos.h",
+    "api/file_system/file_entry_picker.cc",
+    "api/file_system/file_entry_picker.h",
     "api/file_system/file_system_api.cc",
     "api/file_system/file_system_api.h",
     "api/font_settings/font_settings_api.cc",
     "api/font_settings/font_settings_api.h",
     "api/gcm/gcm_api.cc",
     "api/gcm/gcm_api.h",
     "api/history/history_api.cc",
     "api/history/history_api.h",
     "api/hotword_private/hotword_private_api.cc",
     "api/hotword_private/hotword_private_api.h",
@@ skipping 965 matching lines @@
       "api/braille_display_private/brlapi_connection.cc",
       "api/braille_display_private/brlapi_connection.h",
       "api/braille_display_private/brlapi_keycode_map.cc",
       "api/braille_display_private/brlapi_keycode_map.h",
     ]
     deps += [ "//build/linux/libbrlapi" ]
   } else {
     sources += [ "api/braille_display_private/braille_controller_stub.cc" ]
   }
 }