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

Some tests were setting a new key window but failing to restore the original
window after the test concluded.  Leaving the app without a key window breaks
subsequent tests on iOS 9.0, including ContextualSearchJsTest.

BUG=None

Review-Url: https://codereview.chromium.org/2588223002
Cr-Commit-Position: refs/heads/master@{#439679}

ios/chrome/browser/ui/alert_coordinator/alert_coordinator_unittest.mm

@@ -23,12 +23,16 @@
 class AlertCoordinatorTest : public PlatformTest {
  protected:
   AlertCoordinatorTest() {
+    // Save the current key window and restore it after the test.
+    previous_key_window_ = [[UIApplication sharedApplication] keyWindow];
     window_ = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
     [window_ makeKeyAndVisible];
     view_controller_ = [[UIViewController alloc] init];
     [window_ setRootViewController:view_controller_];
   }
 
+  ~AlertCoordinatorTest() override { [previous_key_window_ makeKeyAndVisible]; }
+
   void startAlertCoordinator() { [alert_coordinator_ start]; }
 
   UIViewController* getViewController() { return view_controller_; }
@@ -48,6 +52,7 @@ class AlertCoordinatorTest : public PlatformTest {
   }
 
  private:
+  UIWindow* previous_key_window_;
   AlertCoordinator* alert_coordinator_;
   UIWindow* window_;
   UIViewController* view_controller_;

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_;