Moves maintaining root_window_for_new_windows_ to Shell

ash/test/ash_test_helper.cc

Index: ash/test/ash_test_helper.cc
diff --git a/ash/test/ash_test_helper.cc b/ash/test/ash_test_helper.cc
index 7421eec716f78ca26da957e83c8ad050fefdf6d0..f1a1e5cbab5879a22f2323aefeea82b1fcb630db 100644
--- a/ash/test/ash_test_helper.cc
+++ b/ash/test/ash_test_helper.cc
@@ -227,7 +227,7 @@ TestSessionStateDelegate* AshTestHelper::GetTestSessionStateDelegate() {
 }
 
 aura::Window* AshTestHelper::CurrentContext() {
-  aura::Window* root_window = Shell::GetTargetRootWindow();
+  aura::Window* root_window = Shell::GetRootWindowForNewWindows();
   if (!root_window)
     root_window = Shell::GetPrimaryRootWindow();
   DCHECK(root_window);