Refactors DimWindow and moves to ash/common

ash/wm/screen_dimmer.cc

Index: ash/wm/screen_dimmer.cc
diff --git a/ash/wm/screen_dimmer.cc b/ash/wm/screen_dimmer.cc
index c0bb3d84129f196706530b791342349b78474b88..7e002e52e7277b668d42c3a70cf8e35c5c19b226 100644
--- a/ash/wm/screen_dimmer.cc
+++ b/ash/wm/screen_dimmer.cc
@@ -4,9 +4,10 @@
 
 #include "ash/wm/screen_dimmer.h"
 
+#include "ash/aura/wm_window_aura.h"
+#include "ash/common/wm/window_dimmer.h"
 #include "ash/common/wm_shell.h"
 #include "ash/shell.h"
-#include "ash/wm/dim_window.h"
 #include "base/time/time.h"
 #include "ui/aura/window_event_dispatcher.h"
 #include "ui/aura/window_property.h"
@@ -91,22 +92,19 @@ void ScreenDimmer::OnRootWindowAdded(WmWindow* root_window) {
 
 void ScreenDimmer::Update(bool should_dim) {
   for (aura::Window* container : GetAllContainers(container_id_)) {
-    DimWindow* dim = DimWindow::Get(container);
+    WindowDimmer* dim = WindowDimmer::Get(WmWindowAura::Get(container));
     if (should_dim) {
       if (!dim) {
-        dim = new DimWindow(container);
+        dim = new WindowDimmer(WmWindowAura::Get(container));
         dim->SetDimOpacity(target_opacity_);
       }
       if (at_bottom_)
-        dim->parent()->StackChildAtBottom(dim);
+        dim->parent()->StackChildAtBottom(dim->window());
       else
-        dim->parent()->StackChildAtTop(dim);
-      dim->Show();
-    } else {
-      if (dim) {
-        dim->Hide();
-        delete dim;
-      }
+        dim->parent()->StackChildAtTop(dim->window());
+      dim->window()->Show();
+    } else if (dim) {
+      dim->Destroy();
     }
   }
 }