ash: Do not allow minimizing windows in login screen.

ash/wm/window_util.cc

Index: ash/wm/window_util.cc
diff --git a/ash/wm/window_util.cc b/ash/wm/window_util.cc
index e34af8362785d40ffae45033ef5be342a0c0de2e..a5c694f8a68a0b5350c5aeaf70dcfbc5a128b0b2 100644
--- a/ash/wm/window_util.cc
+++ b/ash/wm/window_util.cc
@@ -7,7 +7,9 @@
 #include <vector>
 
 #include "ash/ash_constants.h"
+#include "ash/root_window_controller.h"
 #include "ash/shell.h"
+#include "ash/shell_window_ids.h"
 #include "ash/wm/activation_controller.h"
 #include "ash/wm/window_properties.h"
 #include "ui/aura/client/activation_client.h"
@@ -66,6 +68,19 @@ bool CanMaximizeWindow(const aura::Window* window) {
   return window->GetProperty(aura::client::kCanMaximizeKey);
 }
 
+bool CanMinimizeWindow(const aura::Window* window) {
+  internal::RootWindowController* controller =
+      internal::RootWindowController::ForWindow(window);
+  if (!controller)
+    return false;
+  aura::Window* lockscreen = controller->GetContainer(
+      internal::kShellWindowId_LockScreenContainersContainer);
+  if (lockscreen->Contains(window))
+    return false;
+
+  return true;
+}
+
 bool CanResizeWindow(const aura::Window* window) {
   return window->GetProperty(aura::client::kCanResizeKey);
 }