opt out dart:ui from nnbd (#16473)

* opt out dart:ui from nnbd

* Annotate tests as well

lib/ui/channel_buffers.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of dart.ui;
 
 /// A saved platform message for a channel with its callback.

lib/ui/compositing.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of dart.ui;
 
 /// An opaque object representing a composited scene.

lib/ui/fixtures/ui_test.dart

+// @dart = 2.6
 // Copyright 2013 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

lib/ui/geometry.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of dart.ui;
 
 /// Base class for [Size] and [Offset], which are both ways to describe

lib/ui/hash_codes.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of dart.ui;
 
 class _HashEnd { const _HashEnd(); }

lib/ui/hooks.dart

@@ -4,6 +4,7 @@
 
 // TODO(dnfield): Remove unused_import ignores when https://github.com/dart-lang/sdk/issues/35164 is resolved.
 
+// @dart = 2.6
 part of dart.ui;
 
 // ignore: unused_element

lib/ui/isolate_name_server.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of dart.ui;
 
 /// Static methods to allow for simple sharing of [SendPort]s across [Isolate]s.

lib/ui/lerp.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of dart.ui;
 
 /// Linearly interpolate between two numbers.

lib/ui/natives.dart

@@ -4,6 +4,7 @@
 
 // TODO(dnfield): remove unused_element ignores when https://github.com/dart-lang/sdk/issues/35164 is resolved.
 
+// @dart = 2.6
 part of dart.ui;
 
 // Corelib 'print' implementation.

lib/ui/painting.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of dart.ui;
 
 // Some methods in this file assert that their arguments are not null. These

lib/ui/plugins.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of dart.ui;
 
 /// A wrapper for a raw callback handle.

lib/ui/pointer.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of dart.ui;
 
 /// How the pointer has changed since the last report.

lib/ui/semantics.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of dart.ui;
 
 /// The possible actions that can be conveyed from the operating system

lib/ui/text.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of dart.ui;
 
 /// Whether to slant the glyphs in the font

lib/ui/ui.dart

@@ -9,6 +9,7 @@
 /// This library exposes the lowest-level services that Flutter frameworks use
 /// to bootstrap applications, such as classes for driving the input, graphics
 /// text, layout, and rendering subsystems.
+// @dart = 2.6
 library dart.ui;
 
 import 'dart:_internal' hide Symbol; // ignore: import_internal_library, unused_import

lib/ui/window.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of dart.ui;
 
 /// Signature of callbacks that have no arguments and return no data.

lib/web_ui/dev/browser.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';

lib/web_ui/dev/build.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 import 'dart:async';
 
 import 'package:args/command_runner.dart';

lib/web_ui/dev/chrome.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 import 'dart:async';
 import 'dart:io';
 

lib/web_ui/dev/chrome_installer.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 import 'dart:io' as io;
 
 import 'package:args/args.dart';

lib/web_ui/dev/clean.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 import 'dart:async';
 import 'dart:io' as io;
 

lib/web_ui/dev/common.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 import 'dart:io' as io;
 
 import 'package:args/args.dart';

lib/web_ui/dev/edge.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 import 'dart:async';
 import 'dart:io';
 

lib/web_ui/dev/edge_installation.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 import 'dart:async';
 import 'dart:io' as io;
 

lib/web_ui/dev/environment.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 import 'dart:io' as io;
 import 'package:path/path.dart' as pathlib;
 

lib/web_ui/dev/felt.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 import 'dart:io' as io;
 
 import 'package:args/command_runner.dart';

lib/web_ui/dev/firefox.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 import 'dart:async';
 import 'dart:io';
 

lib/web_ui/dev/firefox_installer.dart

 // Copyright 2013 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
+// @dart = 2.6
 import 'dart:io' as io;
 
 import 'package:args/args.dart';

lib/web_ui/dev/firefox_installer_test.dart

@@ -4,6 +4,7 @@
 
 @TestOn('vm && linux')
 
+// @dart = 2.6
 import 'dart:io' as io;
 
 import 'package:path/path.dart' as path;

lib/web_ui/dev/goldens.dart

 // Copyright 2013 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
+// @dart = 2.6
 import 'dart:io' as io;
 import 'package:image/image.dart';
 import 'package:meta/meta.dart';

lib/web_ui/dev/licenses.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 import 'dart:io' as io;
 
 import 'package:args/command_runner.dart';

lib/web_ui/dev/safari.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 import 'dart:async';
 import 'dart:io';
 

lib/web_ui/dev/safari_installation.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 import 'dart:async';
 import 'dart:io' as io;
 

lib/web_ui/dev/supported_browsers.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 import 'package:test_api/src/backend/runtime.dart';
 
 import 'browser.dart';

lib/web_ui/dev/test_platform.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';

lib/web_ui/dev/test_runner.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 import 'dart:async';
 import 'dart:io' as io;
 

lib/web_ui/dev/utils.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 import 'dart:async';
 import 'dart:io' as io;
 

lib/web_ui/lib/src/engine.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 library engine;
 
 import 'dart:async';

lib/web_ui/lib/src/engine/alarm_clock.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// A function that returns current system time.

lib/web_ui/lib/src/engine/assets.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// This class downloads assets over the network.

lib/web_ui/lib/src/engine/bitmap_canvas.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// A raw HTML canvas that is directly written to.

lib/web_ui/lib/src/engine/browser_detection.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// The HTML engine used by the current browser.

lib/web_ui/lib/src/engine/browser_location.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 // TODO(mdebbar): add other strategies.

lib/web_ui/lib/src/engine/canvas_pool.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// Allocates and caches 0 or more canvas(s) for [BitmapCanvas].

lib/web_ui/lib/src/engine/clipboard.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// Handles clipboard related platform messages.

lib/web_ui/lib/src/engine/color_filter.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// A description of a color filter to apply when drawing a shape or compositing

lib/web_ui/lib/src/engine/compositor/canvas.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// A Dart wrapper around Skia's SKCanvas.

lib/web_ui/lib/src/engine/compositor/canvas_kit_canvas.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// An implementation of [ui.Canvas] that is backed by a CanvasKit canvas.

lib/web_ui/lib/src/engine/compositor/color_filter.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// A [ui.ColorFilter] backed by Skia's [SkColorFilter].

lib/web_ui/lib/src/engine/compositor/embedded_views.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// This composites HTML views into the [ui.Scene].

lib/web_ui/lib/src/engine/compositor/engine_delegate.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 const String assetChannel = 'flutter/assets';

lib/web_ui/lib/src/engine/compositor/fonts.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 // This URL was found by using the Google Fonts Developer API to find the URL

lib/web_ui/lib/src/engine/compositor/image.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// Instantiates a [ui.Codec] backed by an `SkImage` from Skia.

lib/web_ui/lib/src/engine/compositor/image_filter.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// The CanvasKit implementation of [ui.ImageFilter].

lib/web_ui/lib/src/engine/compositor/initialization.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// EXPERIMENTAL: Enable the Skia-based rendering backend.

lib/web_ui/lib/src/engine/compositor/layer.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// A layer to be composed into a scene.

lib/web_ui/lib/src/engine/compositor/layer_scene_builder.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 class LayerScene implements ui.Scene {

lib/web_ui/lib/src/engine/compositor/layer_tree.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// A tree of [Layer]s that, together with a [Size] compose a frame.

lib/web_ui/lib/src/engine/compositor/n_way_canvas.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// A virtual canvas that applies operations to multiple canvases at once.

lib/web_ui/lib/src/engine/compositor/painting.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// The implementation of [ui.Paint] used by the CanvasKit backend.

lib/web_ui/lib/src/engine/compositor/path.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// An implementation of [ui.Path] which is backed by an `SkPath`.

lib/web_ui/lib/src/engine/compositor/path_metrics.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 class SkPathMetrics extends IterableBase<ui.PathMetric>

lib/web_ui/lib/src/engine/compositor/picture.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 class SkPicture implements ui.Picture {

lib/web_ui/lib/src/engine/compositor/picture_recorder.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 class SkPictureRecorder implements ui.PictureRecorder {

lib/web_ui/lib/src/engine/compositor/platform_message.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 class PlatformMessage {

lib/web_ui/lib/src/engine/compositor/raster_cache.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// A cache of [Picture]s that have already been rasterized.

lib/web_ui/lib/src/engine/compositor/rasterizer.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// A class that can rasterize [LayerTree]s into a given [Surface].

lib/web_ui/lib/src/engine/compositor/runtime_delegate.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 abstract class RuntimeDelegate {

lib/web_ui/lib/src/engine/compositor/surface.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 typedef SubmitCallback = bool Function(SurfaceFrame, SkCanvas);

lib/web_ui/lib/src/engine/compositor/text.dart

 // Copyright 2013 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
+// @dart = 2.6
 part of engine;
 
 class SkParagraphStyle implements ui.ParagraphStyle {

lib/web_ui/lib/src/engine/compositor/util.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// An object backed by a [js.JsObject] mapped onto a Skia C++ object in the

lib/web_ui/lib/src/engine/compositor/vertices.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 Int32List _encodeColorList(List<ui.Color> colors) {

lib/web_ui/lib/src/engine/compositor/viewport_metrics.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 class ViewportMetrics {

lib/web_ui/lib/src/engine/conic.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// Converts conic curve to a list of quadratic curves for rendering on

lib/web_ui/lib/src/engine/dom_canvas.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// A canvas that renders to DOM elements and CSS properties.

lib/web_ui/lib/src/engine/dom_renderer.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 class DomRenderer {

lib/web_ui/lib/src/engine/engine_canvas.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// Defines canvas interface common across canvases that the [SceneBuilder]

lib/web_ui/lib/src/engine/history.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 const MethodCall _popRouteMethodCall = MethodCall('popRoute');

lib/web_ui/lib/src/engine/houdini_canvas.dart

@@ -7,6 +7,7 @@
 // - avoid producing DOM-based clips if there is no text
 // - evaluate using stylesheets for static CSS properties
 // - evaluate reusing houdini canvases
+// @dart = 2.6
 part of engine;
 
 /// A canvas that renders to a combination of HTML DOM and CSS Custom Paint API.

lib/web_ui/lib/src/engine/html_image_codec.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 final bool _supportsDecode = js_util.getProperty(
         js_util.getProperty(

lib/web_ui/lib/src/engine/keyboard.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// Contains a whitelist of keys that must be sent to Flutter under all

lib/web_ui/lib/src/engine/onscreen_logging.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 html.Element _logElement;

lib/web_ui/lib/src/engine/path_to_svg.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// Converts [path] to SVG path syntax to be used as "d" attribute in path

lib/web_ui/lib/src/engine/picture.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// An implementation of [ui.PictureRecorder] backed by a [RecordingCanvas].

lib/web_ui/lib/src/engine/platform_views.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// A registry for factories that create platform views.

lib/web_ui/lib/src/engine/plugins.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 Future<void> Function(String, ByteData, ui.PlatformMessageResponseCallback) pluginMessageCallHandler;

lib/web_ui/lib/src/engine/pointer_binding.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// Set this flag to true to see all the fired events in the console.

lib/web_ui/lib/src/engine/pointer_converter.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 class _PointerState {

lib/web_ui/lib/src/engine/render_vertices.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 _GlRenderer _glRenderer;

lib/web_ui/lib/src/engine/rrect_renderer.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// Renders an RRect using path primitives.

lib/web_ui/lib/src/engine/semantics/accessibility.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// Singleton for accessing accessibility announcements from the platform.

lib/web_ui/lib/src/engine/semantics/checkable.dart

@@ -11,6 +11,7 @@
 //                framework. Currently the framework does not report the
 //                grouping of radio buttons.
 
+// @dart = 2.6
 part of engine;
 
 /// The specific type of checkable control.

lib/web_ui/lib/src/engine/semantics/image.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// Represents semantic objects that deliver information in a visual manner.

lib/web_ui/lib/src/engine/semantics/incrementable.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// Adds increment/decrement event handling to a semantics object.

lib/web_ui/lib/src/engine/semantics/label_and_value.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// Renders [_label] and [_value] to the semantics DOM.

lib/web_ui/lib/src/engine/semantics/live_region.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// Manages semantics configurations that represent live regions.

lib/web_ui/lib/src/engine/semantics/scrollable.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// Implements vertical and horizontal scrolling functionality for semantics

lib/web_ui/lib/src/engine/semantics/semantics.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// Set this flag to `true` to cause the engine to visualize the semantics tree

lib/web_ui/lib/src/engine/semantics/semantics_helper.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// The maximum [semanticsActivationAttempts] before we give up waiting for

lib/web_ui/lib/src/engine/semantics/tappable.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.6
 part of engine;
 
 /// Listens to HTML "click" gestures detected by the browser.