[iOS] Only change action button axis on Sign-in with accessible font.

Updates the requirements for changing the layout axis to display on
a vertical axis when the user turns on "Larger Accessibility Sizes".

Bug: 1110243
Change-Id: Ib4eb3c915298a8cae3606e41c0ea63a2ff1ae062
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2390913Reviewed-by: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Commit-Queue: Nohemi Fernandez <fernandex@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804395}

ios/chrome/browser/ui/authentication/signin/user_signin/user_signin_view_controller.mm

@@ -286,15 +286,22 @@ enum AuthenticationButtonType {
     [NSLayoutConstraint deactivateConstraints:self.compactSizeClassConstraints];
     [NSLayoutConstraint activateConstraints:self.regularSizeClassConstraints];
     fontStyle = UIFontTextStyleTitle2;
-    self.actionButtonsView.axis = UILayoutConstraintAxisHorizontal;
   } else {
     [NSLayoutConstraint deactivateConstraints:self.regularSizeClassConstraints];
     [NSLayoutConstraint activateConstraints:self.compactSizeClassConstraints];
     fontStyle = UIFontTextStyleSubheadline;
-    self.actionButtonsView.axis = UILayoutConstraintAxisVertical;
   }
   [self applyDefaultSizeWithButton:self.confirmationButton fontStyle:fontStyle];
   [self applyDefaultSizeWithButton:self.skipSigninButton fontStyle:fontStyle];
+
+  // For larger texts update the layout to display buttons centered on the
+  // vertical axis.
+  if (UIContentSizeCategoryIsAccessibilityCategory(
+          self.traitCollection.preferredContentSizeCategory)) {
+    self.actionButtonsView.axis = UILayoutConstraintAxisVertical;
+  } else {
+    self.actionButtonsView.axis = UILayoutConstraintAxisHorizontal;
+  }
 }
 
 #pragma mark - Properties