mash: Migrate ScopedTargetRootWindow to //ash/common

ash/wm/window_cycle_controller_unittest.cc

Index: ash/wm/window_cycle_controller_unittest.cc
diff --git a/ash/wm/window_cycle_controller_unittest.cc b/ash/wm/window_cycle_controller_unittest.cc
index 21f02e37d20cfee4b5545a1d570c28d8446c7416..ad61331fc9d2040e3e076c45d4054fcd25f5f6c4 100644
--- a/ash/wm/window_cycle_controller_unittest.cc
+++ b/ash/wm/window_cycle_controller_unittest.cc
@@ -9,6 +9,7 @@
 
 #include "ash/aura/wm_window_aura.h"
 #include "ash/common/focus_cycler.h"
+#include "ash/common/scoped_root_window_for_new_windows.h"
 #include "ash/common/session/session_state_delegate.h"
 #include "ash/common/shell_window_ids.h"
 #include "ash/common/wm/window_cycle_list.h"
@@ -377,8 +378,6 @@ TEST_F(WindowCycleControllerTest, AlwaysOnTopMultipleRootWindows) {
 
   WindowCycleController* controller = WmShell::Get()->window_cycle_controller();
 
-  Shell::GetInstance()->set_target_root_window(root_windows[0]);
-
   // Create two windows in the primary root.
   std::unique_ptr<Window> window0(CreateTestWindowInShellWithId(0));
   EXPECT_EQ(root_windows[0], window0->GetRootWindow());
@@ -387,8 +386,9 @@ TEST_F(WindowCycleControllerTest, AlwaysOnTopMultipleRootWindows) {
   std::unique_ptr<Window> window1(CreateTestWindowWithId(1, top_container0));
   EXPECT_EQ(root_windows[0], window1->GetRootWindow());
 
-  // And two on the secondary root.
-  Shell::GetInstance()->set_target_root_window(root_windows[1]);
+  // Move the active root window to the secondary root and create two windows.
+  ScopedRootWindowForNewWindows root_for_new_windows(
+      WmWindowAura::Get(root_windows[1]));
   std::unique_ptr<Window> window2(CreateTestWindowInShellWithId(2));
   EXPECT_EQ(root_windows[1], window2->GetRootWindow());
 
@@ -397,9 +397,6 @@ TEST_F(WindowCycleControllerTest, AlwaysOnTopMultipleRootWindows) {
   std::unique_ptr<Window> window3(CreateTestWindowWithId(3, top_container1));
   EXPECT_EQ(root_windows[1], window3->GetRootWindow());
 
-  // Move the active root window to the secondary.
-  Shell::GetInstance()->set_target_root_window(root_windows[1]);
-
   wm::ActivateWindow(window2.get());
 
   EXPECT_EQ(root_windows[0], window0->GetRootWindow());