Refactors DimWindow and moves to ash/common

ash/common/wm_window.h

Index: ash/common/wm_window.h
diff --git a/ash/common/wm_window.h b/ash/common/wm_window.h
index 6dfd2cad7ef6a110c7bf055cadf9382b651b3dff..3abddc2ad7816aa7ddefdaec9bb5ac482613d8aa 100644
--- a/ash/common/wm_window.h
+++ b/ash/common/wm_window.h
@@ -64,6 +64,8 @@ class ASH_EXPORT WmWindow {
 
   using Windows = std::vector<WmWindow*>;
 
+  virtual void Destroy() = 0;
+
   WmWindow* GetRootWindow() {
     return const_cast<WmWindow*>(
         const_cast<const WmWindow*>(this)->GetRootWindow());
@@ -161,6 +163,9 @@ class ASH_EXPORT WmWindow {
       std::unique_ptr<WmLayoutManager> layout_manager) = 0;
   virtual WmLayoutManager* GetLayoutManager() = 0;
 
+  // See wm::SetWindowVisibilityChangesAnimated() for details on what this
+  // does.
+  virtual void SetVisibilityChangesAnimated() = 0;
   // |type| is WindowVisibilityAnimationType. Has to be an int to match aura.
   virtual void SetVisibilityAnimationType(int type) = 0;
   virtual void SetVisibilityAnimationDuration(base::TimeDelta delta) = 0;