[iOS] Only show "Cancel Sync" confirmation in Sync & Google Services.

Currently the cancel confirmation alert is shown on all screens
derived from "Sync & Google Services" even if there is no "Cancel"
button on the navigation bar.

Bug: 1115504
Change-Id: I4b8793af8fcb7f7f1bf081d352c18f0f192c6e69
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2358679Reviewed-by: Sergio Collazos <sczs@chromium.org>
Commit-Queue: Nohemi Fernandez <fernandex@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799196}

ios/chrome/browser/ui/authentication/signin/advanced_settings_signin/advanced_settings_signin_coordinator.mm

@@ -251,7 +251,11 @@ using l10n_util::GetNSString;
 
 - (void)presentationControllerDidAttemptToDismiss:
     (UIPresentationController*)presentationController {
-  [self showCancelConfirmationAlert];
+  // Only show cancel confirmation when "Sync and Google Services" is displayed.
+  if (self.googleServicesSettingsCoordinator
+          .googleServicesSettingsViewIsShown) {
+    [self showCancelConfirmationAlert];
+  }
 }
 
 @end

ios/chrome/browser/ui/settings/google_services/google_services_settings_coordinator.h

@@ -33,6 +33,11 @@
     delegate;
 // Presenter which can show signin UI.
 @property(nonatomic, strong) id<ApplicationCommands> handler;
+// Whether the Google services settings view is at the top of the navigation
+// stack. This does not necessarily mean the view is displayed to the user since
+// it can be obstructed by views that are not owned by the navigation stack
+// (e.g. MyGoogle UI).
+@property(nonatomic, assign, readonly) BOOL googleServicesSettingsViewIsShown;
 
 - (instancetype)initWithBaseViewController:(UIViewController*)viewController
                                    browser:(Browser*)browser NS_UNAVAILABLE;

ios/chrome/browser/ui/settings/google_services/google_services_settings_coordinator.mm

@@ -162,6 +162,11 @@ using signin_metrics::PromoAction;
       self.viewController);
 }
 
+- (BOOL)googleServicesSettingsViewIsShown {
+  return [self.viewController
+      isEqual:self.baseNavigationController.topViewController];
+}
+
 #pragma mark - GoogleServicesSettingsCommandHandler
 
 - (void)restartAuthenticationFlow {