Refactors DimWindow and moves to ash/common

ash/BUILD.gn

Index: ash/BUILD.gn
diff --git a/ash/BUILD.gn b/ash/BUILD.gn
index 723a15dc52d7dd1a02bc79dc57ccdda67b0db8f2..c7d9f240802f4dca5599d13ce2d9cf6e5ab34520 100644
--- a/ash/BUILD.gn
+++ b/ash/BUILD.gn
@@ -495,6 +495,8 @@ component("ash") {
     "common/wm/window_cycle_event_filter.h",
     "common/wm/window_cycle_list.cc",
     "common/wm/window_cycle_list.h",
+    "common/wm/window_dimmer.cc",
+    "common/wm/window_dimmer.h",
     "common/wm/window_parenting_utils.cc",
     "common/wm/window_parenting_utils.h",
     "common/wm/window_positioner.cc",
@@ -554,6 +556,7 @@ component("ash") {
     "common/wm_window_observer.h",
     "common/wm_window_property.h",
     "common/wm_window_tracker.h",
+    "common/wm_window_user_data.h",
     "debug.cc",
     "debug.h",
     "default_wallpaper_delegate.cc",
@@ -727,8 +730,6 @@ component("ash") {
     "wm/boot_splash_screen_chromeos.h",
     "wm/cursor_manager_chromeos.cc",
     "wm/cursor_manager_chromeos.h",
-    "wm/dim_window.cc",
-    "wm/dim_window.h",
     "wm/drag_window_controller.cc",
     "wm/drag_window_controller.h",
     "wm/drag_window_resizer.cc",
@@ -1399,6 +1400,7 @@ test("ash_unittests") {
     "common/wm/overview/cleanup_animation_observer_unittest.cc",
     "common/wm/workspace/workspace_event_handler_test_helper.cc",
     "common/wm/workspace/workspace_event_handler_test_helper.h",
+    "common/wm_window_user_data_unittest.cc",
     "dip_unittest.cc",
     "display/cursor_window_controller_unittest.cc",
     "display/display_change_observer_chromeos_unittest.cc",