[ios] Checks Class type for presented Settings VC.

Since some VC's presented by SettingsNavigationController might not be
a SettingsRootTableViewController (e.g. GFBFeedbackViewController) this
CL sets currentPresentedSettingsViewController to nil if this case is true.

Bug: 980037
Change-Id: I5771c27c66820769756ba64b05354b13592e43b0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1807024
Commit-Queue: Sergio Collazos <sczs@chromium.org>
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#696900}

ios/chrome/browser/ui/settings/settings_navigation_controller.mm

@@ -47,7 +47,9 @@ NSString* const kSettingsDoneButtonId = @"kSettingsDoneButtonId";
 @property(nonatomic, strong)
     GoogleServicesSettingsCoordinator* googleServicesSettingsCoordinator;
 
-// Current ViewController being presented by this Navigation Controller.
+// Current SettingsViewController being presented by this Navigation Controller.
+// If nil it means the Navigation Controller is not presenting anything, or the
+// VC being presented is not a SettingsRootTableViewController.
 @property(nonatomic, weak)
     SettingsRootTableViewController* currentPresentedSettingsViewController;
 
@@ -404,8 +406,7 @@ initWithRootViewController:(UIViewController*)rootViewController
       willShowViewController:(UIViewController*)viewController
                     animated:(BOOL)animated {
   self.currentPresentedSettingsViewController =
-      base::mac::ObjCCastStrict<SettingsRootTableViewController>(
-          viewController);
+      base::mac::ObjCCast<SettingsRootTableViewController>(viewController);
 }
 
 #pragma mark - UIResponder