Moves MruWindowTracker to WmShell

ash/wm/overview/window_selector_controller.cc

Index: ash/wm/overview/window_selector_controller.cc
diff --git a/ash/wm/overview/window_selector_controller.cc b/ash/wm/overview/window_selector_controller.cc
index 956a223ce1a36bd2197b345ee1e0f13a92bb6d17..aa4b6da0092161e43eca9fb9a00ead3585844128 100644
--- a/ash/wm/overview/window_selector_controller.cc
+++ b/ash/wm/overview/window_selector_controller.cc
@@ -7,6 +7,7 @@
 #include <vector>
 
 #include "ash/common/session/session_state_delegate.h"
+#include "ash/common/wm/mru_window_tracker.h"
 #include "ash/common/wm/window_state.h"
 #include "ash/common/wm_shell.h"
 #include "ash/common/wm_window.h"
@@ -43,7 +44,8 @@ void WindowSelectorController::ToggleOverview() {
     if (!CanSelect())
       return;
 
-    std::vector<WmWindow*> windows = WmShell::Get()->GetMruWindowList();
+    std::vector<WmWindow*> windows =
+        WmShell::Get()->mru_window_tracker()->BuildMruWindowList();
     auto end =
         std::remove_if(windows.begin(), windows.end(),
                        std::not1(std::ptr_fun(&WindowSelector::IsSelectable)));