Adds physics to the TabBar (#57416) (#57644)

packages/flutter/lib/src/material/tabs.dart

@@ -613,6 +613,7 @@ class TabBar extends StatefulWidget implements PreferredSizeWidget {
     this.dragStartBehavior = DragStartBehavior.start,
     this.mouseCursor,
     this.onTap,
+    this.physics,
   }) : assert(tabs != null),
        assert(isScrollable != null),
        assert(dragStartBehavior != null),
@@ -752,6 +753,14 @@ class TabBar extends StatefulWidget implements PreferredSizeWidget {
   /// interfere with the default tap handler.
   final ValueChanged<int> onTap;
 
+  /// How the [TabBar]'s scroll view should respond to user input.
+  ///
+  /// For example, determines how the scroll view continues to animate after the
+  /// user stops dragging the scroll view.
+  ///
+  /// Defaults to matching platform conventions.
+  final ScrollPhysics physics;
+
   /// A size whose height depends on if the tabs have both icons and text.
   ///
   /// [AppBar] uses this size to compute its own preferred size.
@@ -1115,6 +1124,7 @@ class _TabBarState extends State<TabBar> {
         dragStartBehavior: widget.dragStartBehavior,
         scrollDirection: Axis.horizontal,
         controller: _scrollController,
+        physics: widget.physics,
         child: tabBar,
       );
     }

packages/flutter/test/material/tabs_test.dart

@@ -215,6 +215,11 @@ class TestScrollPhysics extends ScrollPhysics {
     return TestScrollPhysics(parent: buildParent(ancestor));
   }
 
+  @override
+  double applyPhysicsToUserOffset(ScrollMetrics position, double offset) {
+    return offset == 10 ? 20 : offset;
+  }
+
   static final SpringDescription _kDefaultSpring = SpringDescription.withDampingRatio(
     mass: 0.5,
     stiffness: 500.0,
@@ -1108,6 +1113,34 @@ void main() {
     expect(tabController.index, 0);
   });
 
+  testWidgets('TabBar accepts custom physics', (WidgetTester tester) async {
+    final List<Tab> tabs = List<Tab>.generate(20, (int index) {
+      return Tab(text: 'TAB #$index');
+    });
+
+    final TabController controller = TabController(
+      vsync: const TestVSync(),
+      length: tabs.length,
+      initialIndex: tabs.length - 1,
+    );
+
+    await tester.pumpWidget(
+      boilerplate(
+        child: TabBar(
+          isScrollable: true,
+          controller: controller,
+          tabs: tabs,
+          physics: const TestScrollPhysics(),
+        ),
+      ),
+    );
+
+    final TabBar tabBar = tester.widget(find.byType(TabBar));
+    final double position = tabBar.physics.applyPhysicsToUserOffset(null, 10);
+
+    expect(position, equals(20));
+  });
+
   testWidgets('Scrollable TabBar with a non-zero TabController initialIndex', (WidgetTester tester) async {
     // This is a regression test for https://github.com/flutter/flutter/issues/9374