Support floating the header slivers of a NestedScrollView (#59187)

packages/flutter/lib/src/rendering/sliver_persistent_header.dart

@@ -644,7 +644,7 @@ abstract class RenderSliverFloatingPinnedPersistentHeader extends RenderSliverFl
       paintExtent: clampedPaintExtent,
       layoutExtent: layoutExtent.clamp(0.0, clampedPaintExtent) as double,
       maxPaintExtent: maxExtent + stretchOffset,
-      maxScrollObstructionExtent: maxExtent,
+      maxScrollObstructionExtent: minExtent,
       hasVisualOverflow: true, // Conservatively say we do have overflow to avoid complexity.
     );
     return 0.0;

packages/flutter/test/rendering/sliver_persistent_header_test.dart

@@ -26,6 +26,24 @@ void main() {
 
     expect(header.geometry.maxScrollObstructionExtent, 0);
   });
+
+  test('RenderSliverFloatingPinnedPersistentHeader maxScrollObstructionExtent is minExtent', () {
+    final TestRenderSliverFloatingPinnedPersistentHeader header = TestRenderSliverFloatingPinnedPersistentHeader(
+      child: RenderSizedBox(const Size(400.0, 100.0)
+    ));
+    final RenderViewport root = RenderViewport(
+      axisDirection: AxisDirection.down,
+      crossAxisDirection: AxisDirection.right,
+      offset: ViewportOffset.zero(),
+      cacheExtent: 0,
+      children: <RenderSliver>[
+        header,
+      ],
+    );
+    layout(root);
+
+    expect(header.geometry.maxScrollObstructionExtent, 100.0);
+  });
 }
 
 class TestRenderSliverFloatingPersistentHeader extends RenderSliverFloatingPersistentHeader {
@@ -39,3 +57,15 @@ class TestRenderSliverFloatingPersistentHeader extends RenderSliverFloatingPersi
   @override
   double get minExtent => 100;
 }
+
+class TestRenderSliverFloatingPinnedPersistentHeader extends RenderSliverFloatingPinnedPersistentHeader {
+  TestRenderSliverFloatingPinnedPersistentHeader({
+    RenderBox child,
+  }) : super(child: child);
+
+  @override
+  double get maxExtent => 200;
+
+  @override
+  double get minExtent => 100;
+}