[Mac] Check for guest mode correctly before opening the user manager.

BUG=NONE
TBR=asvitkine@chromium.org
TEST=With the --new-profile-management flag, start Chrome. Select
"Browse as guest" from the avatar menu. From the guest browser, select
"View all people" from the avatar menu. This shouldn't crash and should
show the User Manager.

Review URL: https://codereview.chromium.org/129103003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243710 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/ui/cocoa/browser/profile_chooser_controller.mm

@@ -212,8 +212,7 @@ class ActiveProfileObserverBridge : public AvatarMenuObserver,
 - (IBAction)showUserManager:(id)sender {
   // Only non-guest users appear in the User Manager.
   base::FilePath profile_path;
-  // The button tag indicates whether the active profile is a non-guest profile.
-  if ([sender tag]) {
+  if (!isGuestSession_) {
     size_t active_index = avatarMenu_->GetActiveProfileIndex();
     profile_path = avatarMenu_->GetItemAt(active_index).profile_path;
   }