Update app list search box menu when Users changes

ui/app_list/views/search_box_view.cc

Index: ui/app_list/views/search_box_view.cc
diff --git a/ui/app_list/views/search_box_view.cc b/ui/app_list/views/search_box_view.cc
index ba40bf3b5f346c5bac1621c84b4ecafd3abdb9f5..05130cbbf525f4ebf02cb8bae042afc84e1dd88b 100644
--- a/ui/app_list/views/search_box_view.cc
+++ b/ui/app_list/views/search_box_view.cc
@@ -187,8 +187,8 @@ void SearchBoxView::ButtonPressed(views::Button* sender,
 }
 
 void SearchBoxView::OnMenuButtonClicked(View* source, const gfx::Point& point) {
-  if (!menu_)
-    menu_.reset(new AppListMenuViews(view_delegate_));
+  // Always regenerate the menu in case view_delegate_->GetUsers() has changed.

[tapted, 2013/11/26 00:40:07]

So, mac isn't affected by the checkmark-not-moving bug, but it is affected by
the "menu not updated when profile added/removed" bug.

Unfortunately Mac's menu_controller works a bit different -- an `NSMenu` is
populated and attached to the button itself, so I don't think there's a nice way
to intercept the 'click' the way you can for context menus.

But there is already an observer interface -- OnAppListModelSigninStatusChanged
-- which triggers a menu refresh. Hacky fix: just remove the `signed_in_ ==
signed_in` check from

void AppListModel::SetSignedIn(bool signed_in) {
  if (signed_in_ == signed_in)
    return;

/* .. */
}

I think this will fix Mac. Certainly, deleting a profile, then switching the app
launcher to a profile that isn't signed in and back will refresh the menu.

So, to make the fix less hacky, WDYT about just changing
`OnAppListModelSigninStatusChanged` to
`AppListModelObserver::OnAppListModelProfileChanged` ?

It looks like void AppListView::OnSigninStatusChanged() does
`app_list_main_view_->search_box_view()->InvalidateMenu();` so other platforms
should be covered too.

+  menu_.reset(new AppListMenuViews(view_delegate_));
 
   const gfx::Point menu_location =
       menu_button_->GetBoundsInScreen().bottom_right() +