BouncingScrollPhysics should propagate decelerationRate. (#115797)

Author: moffatman

packages/flutter/lib/src/widgets/scroll_physics.dart

@@ -629,7 +629,10 @@ class BouncingScrollPhysics extends ScrollPhysics {
 
   @override
   BouncingScrollPhysics applyTo(ScrollPhysics? ancestor) {
-    return BouncingScrollPhysics(parent: buildParent(ancestor));
+    return BouncingScrollPhysics(
+      parent: buildParent(ancestor),
+      decelerationRate: decelerationRate
+    );
   }
 
   /// The multiple applied to overscroll to make it appear that scrolling past

packages/flutter/test/widgets/scroll_physics_test.dart

@@ -65,6 +65,7 @@ void main() {
     const ScrollPhysics never = NeverScrollableScrollPhysics();
     const ScrollPhysics always = AlwaysScrollableScrollPhysics();
     const ScrollPhysics page = PageScrollPhysics();
+    const ScrollPhysics bounceDesktop = BouncingScrollPhysics(decelerationRate: ScrollDecelerationRate.fast);
 
     String types(ScrollPhysics? value) => value!.parent == null ? '${value.runtimeType}' : '${value.runtimeType} ${types(value.parent)}';
 
@@ -92,6 +93,11 @@ void main() {
       types(page.applyTo(bounce.applyTo(clamp.applyTo(never.applyTo(always))))),
       'PageScrollPhysics BouncingScrollPhysics ClampingScrollPhysics NeverScrollableScrollPhysics AlwaysScrollableScrollPhysics',
     );
+
+    expect(
+      bounceDesktop.applyTo(always),
+      (BouncingScrollPhysics x) => x.decelerationRate == ScrollDecelerationRate.fast
+    );
   });
 
   test("ScrollPhysics scrolling subclasses - Creating the simulation doesn't alter the velocity for time 0", () {