Moves MruWindowTracker to WmShell

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index 67f30356939f9d340f0aa203f4b967c7f978407b..76e6ba10a8f6759a5c6417b490b3320daab4dbe8 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -12,7 +12,6 @@
 #include "ash/accelerators/accelerator_delegate.h"
 #include "ash/accelerators/focus_manager_factory.h"
 #include "ash/ash_switches.h"
-#include "ash/aura/wm_shell_aura.h"
 #include "ash/aura/wm_window_aura.h"
 #include "ash/autoclick/autoclick_controller.h"
 #include "ash/common/session/session_state_delegate.h"
@@ -772,7 +771,7 @@ Shell::~Shell() {
   // MruWindowTracker must be destroyed after all windows have been deleted to
   // avoid a possible crash when Shell is destroyed from a non-normal shutdown
   // path. (crbug.com/485438).
-  mru_window_tracker_.reset();
+  wm_shell_->DeleteMruWindowTracker();
 
   // Chrome implementation of shelf delegate depends on FocusClient,
   // so must be deleted before |focus_client_| (below).
@@ -1048,7 +1047,7 @@ void Shell::Init(const ShellInitParams& init_params) {
 
   magnification_controller_.reset(
       MagnificationController::CreateInstance());
-  mru_window_tracker_.reset(new MruWindowTracker);
+  wm_shell_->CreateMruWindowTracker();
 
   partial_magnification_controller_.reset(
       new PartialMagnificationController());