[supernit] Clarified Property Comment in ConfirmationAlertViewController

Merged the previous CL too quickly.

Bug: 1064990
Change-Id: Icb98433f1ab7daebc7cd5ef4190e1610b05a519d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2163145
Commit-Queue: Sebastien Lalancette <seblalancette@chromium.org>
Commit-Queue: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Auto-Submit: Sebastien Lalancette <seblalancette@chromium.org>
Reviewed-by: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Cr-Commit-Position: refs/heads/master@{#761976}

ios/chrome/common/ui/confirmation_alert/confirmation_alert_view_controller.h

@@ -49,7 +49,7 @@ extern NSString* const
 @property(nonatomic) BOOL alwaysShowImage;
 
 // The style of the primary action button added to the toolbar. Must be set if
-// alwaysShowImage is set to YES.
+// both alwaysShowImage and primaryActionAvailable are set to YES.
 @property(nonatomic) UIBarButtonSystemItem primaryActionBarButtonStyle;
 
 // Controls if there is a help button in the view. Must be set before the