[ios] Restore the original key window at the end of the AlertCoordinator tests.

ios/chrome/browser/ui/context_menu/context_menu_coordinator_unittest.mm

Index: ios/chrome/browser/ui/context_menu/context_menu_coordinator_unittest.mm
diff --git a/ios/chrome/browser/ui/context_menu/context_menu_coordinator_unittest.mm b/ios/chrome/browser/ui/context_menu/context_menu_coordinator_unittest.mm
index be724fc1061b4d592532a5f05a004019c121d9a1..5ef3dac4a8d6663f3e6ed7a6983f09b8711ca4a7 100644
--- a/ios/chrome/browser/ui/context_menu/context_menu_coordinator_unittest.mm
+++ b/ios/chrome/browser/ui/context_menu/context_menu_coordinator_unittest.mm
@@ -16,6 +16,9 @@
 class ContextMenuCoordinatorTest : public PlatformTest {
  public:
   ContextMenuCoordinatorTest() {
+    // Save the current key window and restore it after the test.
+    previous_key_window_.reset(
+        [[[UIApplication sharedApplication] keyWindow] retain]);
     window_.reset(
         [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]]);
     [window_ makeKeyAndVisible];
@@ -23,7 +26,12 @@ class ContextMenuCoordinatorTest : public PlatformTest {
     [window_ setRootViewController:view_controller_];
   }
 
+  ~ContextMenuCoordinatorTest() override {
+    [previous_key_window_ makeKeyAndVisible];
+  }
+
  protected:
+  base::scoped_nsobject<UIWindow> previous_key_window_;
   base::scoped_nsobject<ContextMenuCoordinator> menu_coordinator_;
   base::scoped_nsobject<UIWindow> window_;
   base::scoped_nsobject<UIViewController> view_controller_;