Promote WidgetTester.ensureVisible to WidgetController (#61540)

* Promtoe WidgetTester.ensureVisible

* modify according to tvolkert@

packages/flutter_test/lib/src/controller.dart

@@ -676,6 +676,20 @@ abstract class WidgetController {
   /// Returns the rect of the given widget. This is only valid once
   /// the widget's render object has been laid out at least once.
   Rect getRect(Finder finder) => getTopLeft(finder) & getSize(finder);
+
+  /// Given a widget `W` specified by [finder] and a [Scrollable] widget `S` in
+  /// its ancestry tree, this scrolls `S` so as to make `W` visible.
+  ///
+  /// Usually the `finder` for this method should be labeled
+  /// `skipOffstage: false`, so that [Finder] deals with widgets that's out of
+  /// the screen correctly.
+  ///
+  /// This does not work when the `S` is long and `W` far away from the
+  /// dispalyed part does not have a cached element yet. See
+  /// https://github.com/flutter/flutter/issues/61458
+  ///
+  /// Shorthand for `Scrollable.ensureVisible(element(finder))`
+  Future<void> ensureVisible(Finder finder) => Scrollable.ensureVisible(element(finder));
 }
 
 /// Variant of [WidgetController] that can be used in tests running

packages/flutter_test/lib/src/widget_tester.dart

@@ -1128,12 +1128,6 @@ class WidgetTester extends WidgetController implements HitTestDispatcher, Ticker
   SemanticsHandle ensureSemantics() {
     return binding.pipelineOwner.ensureSemantics();
   }
-
-  /// Given a widget `W` specified by [finder] and a [Scrollable] widget `S` in
-  /// its ancestry tree, this scrolls `S` so as to make `W` visible.
-  ///
-  /// Shorthand for `Scrollable.ensureVisible(tester.element(finder))`
-  Future<void> ensureVisible(Finder finder) => Scrollable.ensureVisible(element(finder));
 }
 
 typedef _TickerDisposeCallback = void Function(_TestTicker ticker);

packages/flutter_test/test/controller_test.dart

@@ -414,4 +414,29 @@ void main() {
       }
     },
   );
+
+  testWidgets(
+    'ensureVisibl: scrolls to make widget visible',
+    (WidgetTester tester) async {
+      await tester.pumpWidget(
+        MaterialApp(
+          home: Scaffold(
+            body: ListView.builder(
+              itemCount: 20,
+              shrinkWrap: true,
+              itemBuilder: (BuildContext context, int i) => ListTile(title: Text('Item $i')),
+            ),
+          ),
+        ),
+      );
+
+      // Make sure widget isn't on screen
+      expect(find.text('Item 15', skipOffstage: true), findsNothing);
+
+      await tester.ensureVisible(find.text('Item 15', skipOffstage: false));
+      await tester.pumpAndSettle();
+
+      expect(find.text('Item 15', skipOffstage: true), findsOneWidget);
+    },
+  );
 }

packages/flutter_test/test/widget_tester_test.dart

@@ -158,30 +158,6 @@ void main() {
     });
   });
 
-  group('ensureVisible', () {
-    testWidgets('scrolls to make widget visible', (WidgetTester tester) async {
-      await tester.pumpWidget(
-        MaterialApp(
-          home: Scaffold(
-            body: ListView.builder(
-              itemCount: 20,
-              shrinkWrap: true,
-              itemBuilder: (BuildContext context, int i) => ListTile(title: Text('Item $i')),
-           ),
-         ),
-        ),
-      );
-
-      // Make sure widget isn't on screen
-      expect(find.text('Item 15', skipOffstage: true), findsNothing);
-
-      await tester.ensureVisible(find.text('Item 15', skipOffstage: false));
-      await tester.pumpAndSettle();
-
-      expect(find.text('Item 15', skipOffstage: true), findsOneWidget);
-    });
-  });
-
   group('expectLater', () {
     testWidgets('completes when matcher completes', (WidgetTester tester) async {
       final Completer<void> completer = Completer<void>();