Refactor backdrop that is currently used in the maximized mode.

ash/BUILD.gn

Index: ash/BUILD.gn
diff --git a/ash/BUILD.gn b/ash/BUILD.gn
index a89820ed43e5ccbe1573d09903b2b2c959872975..0570a82af796e357f7b3b97ce1c091b8c394c18b 100644
--- a/ash/BUILD.gn
+++ b/ash/BUILD.gn
@@ -658,6 +658,8 @@ component("ash") {
     "wm/lock_state_observer.h",
     "wm/lock_window_state.cc",
     "wm/lock_window_state.h",
+    "wm/maximize_mode/maximize_mode_backdrop_delegate_impl.cc",
+    "wm/maximize_mode/maximize_mode_backdrop_delegate_impl.h",
     "wm/maximize_mode/maximize_mode_controller.cc",
     "wm/maximize_mode/maximize_mode_controller.h",
     "wm/maximize_mode/maximize_mode_event_handler.cc",
@@ -673,8 +675,6 @@ component("ash") {
     "wm/maximize_mode/scoped_disable_internal_mouse_and_keyboard_ozone.h",
     "wm/maximize_mode/scoped_disable_internal_mouse_and_keyboard_x11.cc",
     "wm/maximize_mode/scoped_disable_internal_mouse_and_keyboard_x11.h",
-    "wm/maximize_mode/workspace_backdrop_delegate.cc",
-    "wm/maximize_mode/workspace_backdrop_delegate.h",
     "wm/mru_window_tracker.cc",
     "wm/mru_window_tracker.h",
     "wm/overlay_event_filter.cc",
@@ -794,6 +794,9 @@ component("ash") {
     "wm/wm_types.h",
     "wm/wm_window_animations.cc",
     "wm/wm_window_animations.h",
+    "wm/workspace/backdrop_controller.cc",
+    "wm/workspace/backdrop_controller.h",
+    "wm/workspace/backdrop_delegate.h",
     "wm/workspace/magnetism_matcher.cc",
     "wm/workspace/magnetism_matcher.h",
     "wm/workspace/multi_window_resize_controller.cc",
@@ -808,7 +811,6 @@ component("ash") {
     "wm/workspace/workspace_event_handler_aura.h",
     "wm/workspace/workspace_layout_manager.cc",
     "wm/workspace/workspace_layout_manager.h",
-    "wm/workspace/workspace_layout_manager_backdrop_delegate.h",
     "wm/workspace/workspace_types.h",
     "wm/workspace/workspace_window_resizer.cc",
     "wm/workspace/workspace_window_resizer.h",