Moves MruWindowTracker to WmShell

ash/common/wm_shell.h

Index: ash/common/wm_shell.h
diff --git a/ash/common/wm_shell.h b/ash/common/wm_shell.h
index d111540cf7da655c1051edc4375f327ee5cfff7b..00b62accc51eea52d3d44f1c9e9f3313d47f9e53 100644
--- a/ash/common/wm_shell.h
+++ b/ash/common/wm_shell.h
@@ -18,6 +18,8 @@ class Rect;
 
 namespace ash {
 
+class Shell;
+class MruWindowTracker;
 class SessionStateDelegate;
 class WindowResizer;
 class WmActivationObserver;
@@ -35,13 +37,13 @@ enum class WmUserMetricsAction;
 // Similar to ash::Shell. Eventually the two will be merged.
 class ASH_EXPORT WmShell {
  public:
-  virtual ~WmShell() {}
-
   // This is necessary for a handful of places that is difficult to plumb
   // through context.
   static void Set(WmShell* instance);
   static WmShell* Get();
 
+  MruWindowTracker* mru_window_tracker() { return mru_window_tracker_.get(); }
+
   // Creates a new window used as a container of other windows. No painting is
   // done to the created window.
   virtual WmWindow* NewContainerWindow() = 0;
@@ -59,12 +61,6 @@ class ASH_EXPORT WmShell {
   // appropriate container in the returned window.
   virtual WmWindow* GetRootWindowForNewWindows() = 0;
 
-  // Returns the list of most recently used windows.
-  virtual std::vector<WmWindow*> GetMruWindowList() = 0;
-
-  // Returns the list of most recently used windows excluding modals.
-  virtual std::vector<WmWindow*> GetMruWindowListIgnoreModals() = 0;
-
   // Returns true if the first window shown on first run should be
   // unconditionally maximized, overriding the heuristic that normally chooses
   // the window size.
@@ -106,8 +102,19 @@ class ASH_EXPORT WmShell {
   virtual void AddOverviewModeObserver(WmOverviewModeObserver* observer) = 0;
   virtual void RemoveOverviewModeObserver(WmOverviewModeObserver* observer) = 0;
 
+ protected:
+  WmShell();
+  virtual ~WmShell();
+
+  void CreateMruWindowTracker();
+  void DeleteMruWindowTracker();
+
  private:
+  friend class Shell;
+
   static WmShell* instance_;
+
+  std::unique_ptr<MruWindowTracker> mru_window_tracker_;
 };
 
 }  // namespace ash