Remove snap scrolling test (#8117)

The new scrolling machinery doesn't support snap scrolling.

packages/flutter/test/widgets/snap_scrolling_test.dart

-// Copyright 2015 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 'dart:async';
-
-import 'package:flutter_test/flutter_test.dart';
-import 'package:flutter/widgets.dart';
-
-const double itemExtent = 200.0;
-Axis scrollDirection = Axis.vertical;
-
-Widget buildItem(int item) {
-  return new Container(
-    width: itemExtent,
-    height: itemExtent,
-    child: new Text(item.toString())
-  );
-}
-
-double snapOffsetCallback(double offset, Size size) {
-  return (offset / itemExtent).floor() * itemExtent;
-}
-
-class TestScrollConfigurationDelegate extends ScrollConfigurationDelegate {
-  const TestScrollConfigurationDelegate();
-
-  // Not testing platform-specific fling scrolling, use the default fling
-  // decleration simulation.
-  @override
-  TargetPlatform get platform => null;
-
-  @override
-  ExtentScrollBehavior createScrollBehavior() => new OverscrollWhenScrollableBehavior(platform: platform);
-
-  @override
-  bool updateShouldNotify(ScrollConfigurationDelegate old) => false;
-}
-
-Widget buildFrame() {
-  return new ScrollConfiguration(
-    delegate: const TestScrollConfigurationDelegate(),
-    child: new Center(
-      child: new Container(
-        height: itemExtent * 2.0,
-        child: new ScrollableList(
-          snapOffsetCallback: snapOffsetCallback,
-          scrollDirection: scrollDirection,
-          itemExtent: itemExtent,
-          children: <int>[0, 1, 2, 3, 4, 5, 7, 8, 9].map(buildItem)
-        )
-      )
-    )
-  );
-}
-
-void main() {
-  testWidgets('ScrollableList snap scrolling', (WidgetTester tester) async {
-    ScrollableState getScrollableState() => tester.state(find.byType(Scrollable));
-
-    double getScrollOffset() => getScrollableState().scrollOffset;
-    void setScrollOffset(double value) {
-      getScrollableState().scrollTo(value);
-    }
-
-    Completer<Null> fling(double velocity) {
-      Completer<Null> completer = new Completer<Null>();
-      getScrollableState().fling(velocity).whenComplete(completer.complete);
-      return completer;
-    }
-
-    await tester.pumpWidget(buildFrame());
-
-    setScrollOffset(0.0);
-    await tester.pump();
-    expect(getScrollOffset(), 0.0);
-
-    Duration dt = const Duration(seconds: 2);
-
-    Completer<Null> completer = fling(1000.0);
-    expect(completer.isCompleted, isFalse);
-    await tester.pump(); // Start the scheduler at 0.0
-    await tester.pump(dt);
-    expect(getScrollOffset(), closeTo(200.0, 1.0));
-    expect(completer.isCompleted, isTrue);
-
-    setScrollOffset(0.0);
-    await tester.pump();
-    expect(getScrollOffset(), 0.0);
-
-    completer = fling(2000.0);
-    expect(completer.isCompleted, isFalse);
-    await tester.pump();
-    await tester.pump(dt);
-    expect(getScrollOffset(), closeTo(400.0, 1.0));
-    expect(completer.isCompleted, isTrue);
-
-    setScrollOffset(400.0);
-    await tester.pump();
-    expect(getScrollOffset(), 400.0);
-
-    completer = fling(-800.0);
-    expect(completer.isCompleted, isFalse);
-    await tester.pump();
-    await tester.pump(dt);
-    expect(getScrollOffset(), closeTo(0.0, 1.0));
-    expect(completer.isCompleted, isTrue);
-
-    setScrollOffset(800.0);
-    await tester.pump();
-    expect(getScrollOffset(), 800.0);
-
-    completer = fling(-2000.0);
-    expect(completer.isCompleted, isFalse);
-    await tester.pump();
-    await tester.pump(dt);
-    expect(getScrollOffset(), closeTo(200.0, 1.0));
-    expect(completer.isCompleted, isTrue);
-
-    setScrollOffset(800.0);
-    await tester.pump();
-    expect(getScrollOffset(), 800.0);
-
-    completer = fling(-2000.0);
-    expect(completer.isCompleted, isFalse);
-    await tester.pump();
-    await tester.pump(dt);
-    expect(completer.isCompleted, isTrue);
-    expectSync(getScrollOffset(), closeTo(200.0, 1.0));
-  });
-}