[Shell] BackButtonBehavior is used to override the icon

[davidortinau]

Description

This is done to override the back button.

var bbb = new BackButtonBehavior()
            {
                IconOverride = ImageSource.FromFile("close")
            };

            Shell.SetBackButtonBehavior(this, bbb);

"Behavior" here seems odd to me. Doesn't seem like a behavior.

Also when I do this, it replaces the hamburger, but also doesn't open the menu.

Expected Behavior

I can set the icon on a property of the Shell, a Style, or on the ContentPage.

Actual Behavior

I can only set in code like above via a behavior.

Basic Information

• Version with issue: 4.0-pre1

Screenshots

https://www.screencast.com/t/TFrhknPNYhz3
Parent: #2415