Remove RenderBlockViewport

Previously this was used by MixedViewport, but now we don't need it because

LazyBlockViewport has replaced MixedViewport.



I've also taken this opportunity to modernize RenderBlock.

packages/flutter/test/rendering/block_test.dart

@@ -2,17 +2,9 @@
 // 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/rendering.dart';
 import 'package:test/test.dart';
 
-import 'rendering_tester.dart';
-
-class TestBlockPainter extends RenderObjectPainter {
-  @override
-  void paint(PaintingContext context, Offset offset) { }
-}
-
 void main() {
   test('block intrinsics', () {
     RenderParagraph paragraph = new RenderParagraph(
@@ -58,30 +50,4 @@ void main() {
     expect(testBlock.getMinIntrinsicHeight(empty), equals(0.0));
     expect(testBlock.getMaxIntrinsicHeight(empty), equals(0.0));
   });
-
-
-  test('overlay painters can attach and detach', () {
-    TestBlockPainter first = new TestBlockPainter();
-    TestBlockPainter second = new TestBlockPainter();
-    RenderBlockViewport block = new RenderBlockViewport(overlayPainter: first);
-
-    // The first painter isn't attached because we haven't attached block.
-    expect(first.renderObject, isNull);
-    expect(second.renderObject, isNull);
-
-    block.overlayPainter = second;
-
-    expect(first.renderObject, isNull);
-    expect(second.renderObject, isNull);
-
-    layout(block);
-
-    expect(first.renderObject, isNull);
-    expect(second.renderObject, equals(block));
-
-    block.overlayPainter = first;
-
-    expect(first.renderObject, equals(block));
-    expect(second.renderObject, isNull);
-  });
 }

packages/flutter/test/rendering/list_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 'package:flutter/rendering.dart';
+import 'package:test/test.dart';
+
+import 'rendering_tester.dart';
+
+class TestBlockPainter extends RenderObjectPainter {
+  @override
+  void paint(PaintingContext context, Offset offset) { }
+}
+
+void main() {
+  test('overlay painters can attach and detach', () {
+    TestBlockPainter first = new TestBlockPainter();
+    TestBlockPainter second = new TestBlockPainter();
+    RenderList list = new RenderList(overlayPainter: first);
+
+    // The first painter isn't attached because we haven't attached block.
+    expect(first.renderObject, isNull);
+    expect(second.renderObject, isNull);
+
+    list.overlayPainter = second;
+
+    expect(first.renderObject, isNull);
+    expect(second.renderObject, isNull);
+
+    layout(list);
+
+    expect(first.renderObject, isNull);
+    expect(second.renderObject, equals(list));
+
+    list.overlayPainter = first;
+
+    expect(first.renderObject, equals(list));
+    expect(second.renderObject, isNull);
+  });
+}