Fix overlay_geometry manual test. (#13315)

Somehow the test ended up checking for notification messages at the wrong depth.

dev/manual_tests/lib/overlay_geometry.dart

@@ -152,7 +152,7 @@ class OverlayGeometryAppState extends State<OverlayGeometryApp> {
   }
 
   bool handleScrollNotification(ScrollNotification notification) {
-    if (notification is ScrollUpdateNotification && notification.depth == 1) {
+    if (notification is ScrollUpdateNotification && notification.depth == 0) {
       setState(() {
         final double dy = markersScrollOffset - notification.metrics.extentBefore;
         markersScrollOffset = notification.metrics.extentBefore;

dev/manual_tests/test/overlay_geometry_test.dart

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import '../lib/overlay_geometry.dart' as overlay_geometry;
+
+void main() {
+  testWidgets('Overlay geometry smoke test', (WidgetTester tester) async {
+    await tester.pumpWidget(new MaterialApp(home: new overlay_geometry.OverlayGeometryApp()));
+    expect(find.byType(overlay_geometry.Marker), findsNothing);
+    await tester.tap(find.text('Card 3'));
+    await tester.pump();
+    expect(find.byType(overlay_geometry.Marker), findsNWidgets(3));
+    final double y = tester.getTopLeft(find.byType(overlay_geometry.Marker).first).dy;
+    await tester.fling(find.text('Card 3'), const Offset(0.0, -100.0), 100.0);
+    await tester.pump();
+    expect(find.byType(overlay_geometry.Marker), findsNWidgets(3));
+    expect(tester.getTopLeft(find.byType(overlay_geometry.Marker).first).dy, lessThan(y));
+  });
+}