The number of physical pixels on each side of the display rectangle into which the application can render, but which may be partially obscured by system UI (such as the system notification area), or or physical intrusions in the display (e.g. overscan regions on television screens or phone sensor housings).
This value is calculated by taking
max(0.0, Window.viewPadding - Window.viewInsets). This will treat a
system IME that increases the bottom inset as consuming that much of the
bottom padding. For example, on an iPhone X,
the same as
Window.viewPadding.bottom when the soft keyboard is not
drawn (to account for the bottom soft button area), but will be
the soft keyboard is visible.
When this changes, onMetricsChanged is called.
@override WindowPadding get padding => _paddingTestValue ?? _window.padding;