Divide volume_manager.js into files for each classes and extract interfaces from them.

ui/file_manager/gallery/js/compiled_resources.gyp

 # 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.
 {
   'targets': [
     {
       'target_name': 'background',
       'variables': {
         'depends': [
           '../../../../third_party/jstemplate/compiled_resources.gyp:jstemplate',
           '../../../webui/resources/js/cr.js',
           '../../../webui/resources/js/cr/event_target.js',
           '../../../webui/resources/js/cr/ui.js',
           '../../../webui/resources/js/cr/ui/array_data_model.js',
           '../../../webui/resources/js/load_time_data.js',
           '../../../webui/resources/js/promise_resolver.js',
           '../../../webui/resources/js/util.js',
           '../../file_manager/common/js/util.js',
           '../../file_manager/common/js/async_util.js',
           '../../file_manager/common/js/volume_manager_common.js',
           '../../file_manager/common/js/error_util.js',
           '../../file_manager/common/js/file_type.js',
           '../../file_manager/common/js/metrics_base.js',
           '../../file_manager/common/js/metrics_events.js',
           '../../file_manager/common/js/metrics.js',
           '../../file_manager/background/js/app_window_wrapper.js',
           '../../file_manager/background/js/background_base.js',
-          '../../file_manager/background/js/volume_manager.js',
+          '../../file_manager/background/js/entry_location_impl.js',
+          '../../file_manager/background/js/volume_info_impl.js',
+          '../../file_manager/background/js/volume_info_list_impl.js',
+          '../../file_manager/background/js/volume_manager_factory.js',
+          '../../file_manager/background/js/volume_manager_impl.js',
+          '../../file_manager/background/js/volume_manager_util.js',
         ],
         'externs': [
           '<(EXTERNS_DIR)/chrome_extensions.js',
           '<(EXTERNS_DIR)/chrome_send.js',
           '<(EXTERNS_DIR)/file_manager_private.js',
           '<(EXTERNS_DIR)/metrics_private.js',
           '../../../../third_party/analytics/externs.js',
           '../../externs/chrome_test.js',
+          '../../externs/entry_location.js',
           '../../externs/es6_workaround.js',
           '../../externs/gallery_background.js',
           '../../externs/platform.js',
           '../../externs/volume_info.js',
+          '../../externs/volume_info_list.js',
+          '../../externs/volume_manager.js',
         ],
       },
       'includes': [
         '../../compile_js.gypi',
       ],
     },
     {
       'target_name': 'gallery',
       'variables': {
         'depends': [
@@ skipping 52 matching lines @@
           '../../file_manager/foreground/js/metadata/metadata_model.js',
           '../../file_manager/foreground/js/metadata/metadata_provider.js',
           '../../file_manager/foreground/js/metadata/multi_metadata_provider.js',
           '../../file_manager/foreground/js/metadata/thumbnail_model.js',
           '../../file_manager/foreground/js/share_client.js',
           '../../file_manager/foreground/js/thumbnail_loader.js',
           '../../file_manager/foreground/js/ui/file_manager_dialog_base.js',
           '../../file_manager/foreground/js/ui/files_confirm_dialog.js',
           '../../file_manager/foreground/js/ui/share_dialog.js',
           '../../file_manager/foreground/js/volume_manager_wrapper.js',
-          '../../file_manager/background/js/volume_manager.js',
           '../../image_loader/image_loader_client.js',
           './image_editor/image_util.js',
           './image_editor/viewport.js',
           './image_editor/image_buffer.js',
           './image_editor/image_view.js',
           './image_editor/commands.js',
           './image_editor/image_editor.js',
           './image_editor/image_transform.js',
           './image_editor/image_adjust.js',
           './image_editor/filter.js',
           './image_editor/image_encoder.js',
           './image_editor/exif_encoder.js',
           './dimmable_ui_controller.js',
           './entry_list_watcher.js',
           './error_banner.js',
           './gallery_data_model.js',
           './gallery_item.js',
           './gallery_util.js',
           './ribbon.js',
           './slide_mode.js',
           './thumbnail_mode.js',
         ],
         'externs': [
           '<(EXTERNS_DIR)/chrome_extensions.js',
           '<(EXTERNS_DIR)/chrome_send.js',
           '<(EXTERNS_DIR)/file_manager_private.js',
           '<(EXTERNS_DIR)/metrics_private.js',
           '../../../../third_party/analytics/externs.js',
           '../../../../third_party/closure_compiler/externs/polymer-1.0.js',
+          '../../externs/background_window_common.js',
           '../../externs/chrome_test.js',
+          '../../externs/entry_location.js',
           '../../externs/es6_workaround.js',
           '../../externs/exif_entry.js',
           '../../externs/files_elements.js',
           '../../externs/gallery_foreground.js',
           '../../externs/paper_elements.js',
           '../../externs/platform.js',
           '../../externs/volume_info.js',
+          '../../externs/volume_info_list.js',
+          '../../externs/volume_manager.js',
           '../../externs/webview_tag.js',
         ],
       },
       'includes': [
         '../../compile_js.gypi',
       ],
     }
   ],
 }