## The bug
Repro steps:
1. Open MDCDragons on an iPhone with a notch.
2. Open App Bar -> Presented hidden.
3. Present the App Bar.
4. Observe.
Expected behavior:
- The AppBar is completely hidden.
Actual behavior:
- The AppBar is partially hidden.
## Root cause analysis
When the FlexibleHeader is hidden using shiftHeaderOffScreenAnimated:, the expectation is that the header will be shifted entirely off-screen. If this method is invoked before the FlexibleHeader is attached to a window hierarchy, then the offset applied to shift the header off-screen may not correctly include the necessary safe area insets to hide the header fully.
When flexibleHeaderSafeAreaTopSafeAreaInsetDidChange was being invoked after the safe area insets were made available to the FlexibleHeader, we were not taking into consideration whether the FlexibleHeader was supposed to be hidden which resulted in the FlexibleHeader getting stuck in a partially hidden state.
## The fix
In flexibleHeaderSafeAreaTopSafeAreaInsetDidChange, we now check whether the FlexibleHeader wants to be hidden and, if it does (and we're not already animating it), we immediately snap the FlexibleHeader to the new necessary offset.
PiperOrigin-RevId: 311104051
The example was reusing the same view controller instance after each presentation, which made it difficult to consistently test the same buggy behavior.
PiperOrigin-RevId: 310980123
This example demonstrates a bug where the AppBar does not appear to respect shiftHeaderOffScreenAnimated: when the shiftBehavior is set to hideable.
PiperOrigin-RevId: 310898136
