ash: Do not allow minimizing windows in login screen.

ash/accelerators/accelerator_controller.cc

Index: ash/accelerators/accelerator_controller.cc
diff --git a/ash/accelerators/accelerator_controller.cc b/ash/accelerators/accelerator_controller.cc
index 530f8d35a2d36329c302b881c6e715f036428cdd..d1001f2f9ca854efc4707ac03299a2595916a1c8 100644
--- a/ash/accelerators/accelerator_controller.cc
+++ b/ash/accelerators/accelerator_controller.cc
@@ -715,7 +715,7 @@ bool AcceleratorController::PerformAction(int action,
       // Disable the shortcut for minimizing full screen window due to
       // crbug.com/131709, which is a crashing issue related to minimizing
       // full screen pepper window.
-      if (!wm::IsWindowFullscreen(window)) {
+      if (!wm::IsWindowFullscreen(window) && wm::CanMinimizeWindow(window)) {
         wm::MinimizeWindow(window);
         return true;
       }