Add regression test for treeshaking debugFillProperties (#17325)

* Add test to make sure we don't regress treeshaking of debugFillProperties
* update cirrus

.cirrus.yml

@@ -156,6 +156,7 @@ task:
         - $FRAMEWORK_PATH/flutter/bin/flutter config --local-engine=host_debug_unopt --no-analytics --enable-web
         - $FRAMEWORK_PATH/flutter/bin/flutter pub get --local-engine=host_debug_unopt
         - $FRAMEWORK_PATH/flutter/bin/flutter drive -v --target=test_driver/text_editing_e2e.dart -d web-server --release --browser-name=chrome --local-engine=host_debug_unopt
+        - $FRAMEWORK_PATH/flutter/bin/flutter drive -v --target=test_driver/treeshaking_e2e.dart -d web-server --profile --browser-name=chrome --local-engine=host_debug_unopt
         - $FRAMEWORK_PATH/flutter/bin/flutter drive -v --target=test_driver/image_loading_e2e.dart -d web-server --release --browser-name=chrome --local-engine=host_debug_unopt
 
     - name: build_and_test_web_linux_firefox

e2etests/web/regular_integration_tests/lib/treeshaking_main.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.
+
+import 'package:flutter/material.dart';
+
+void main() => runApp(MyApp());
+
+class MyApp extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      key: const Key('mainapp'),
+      title: 'Integration Test App',
+      home: MyHomePage(title: 'Integration Test App'),
+    );
+  }
+}
+
+class MyHomePage extends StatefulWidget {
+  MyHomePage({Key key, this.title}) : super(key: key);
+
+  final String title;
+
+  @override
+  _MyHomePageState createState() => _MyHomePageState();
+}
+
+class _MyHomePageState extends State<MyHomePage> {
+  final TextEditingController _controller =
+  TextEditingController(text: 'TreeshakingThings1');
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: Text(widget.title),
+      ),
+      body: const Center(
+        child: Text('TreeshakingThings'),
+      ),
+    );
+  }
+}

e2etests/web/regular_integration_tests/test_driver/treeshaking_e2e.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.
+
+import 'dart:html' as html;
+import 'package:flutter_test/flutter_test.dart';
+import 'package:regular_integration_tests/treeshaking_main.dart' as app;
+import 'package:flutter/material.dart';
+
+import 'package:e2e/e2e.dart';
+
+void main() {
+  E2EWidgetsFlutterBinding.ensureInitialized() as E2EWidgetsFlutterBinding;
+
+  testWidgets('debug+Fill+Properties for widgets is tree shaken',
+          (WidgetTester tester) async {
+    // About 11 instances are used by DiagnosticsNode and diagnostics
+    // for flutter framework itself. Widgets have > 100. So we check for 20 to
+    // so this test fails when tree-shaking is broken.
+    await testOccurenceCountBelow(tester, '${debugPrefix}FillProperties', 20);
+  });
+}
+
+// Used to prevent compiler optimization that will generate const string.
+// Preventing counting test strings.
+String get debugPrefix => <String>['d','e','b','u','g'].join('');
+
+Future<void> testOccurenceCountBelow(WidgetTester tester, String methodName, int count) async {
+  app.main();
+  await tester.pumpAndSettle();
+
+  // Make sure app loaded.
+  final Finder finder = find.byKey(const Key('mainapp'));
+  expect(finder, findsOneWidget);
+
+  await _loadBundleAndCheck(methodName, count);
+}
+
+String fileContents;
+
+Future<void> _loadBundleAndCheck(String methodName, int count) async {
+  fileContents ??= await html.HttpRequest.getString('main.dart.js');
+  expect(fileContents, contains('RenderObjectToWidgetElement'));
+  expect(occurrenceCount(fileContents, methodName), lessThan(count));
+}
+
+int occurrenceCount(String contents, String word) {
+  int count = 0;
+  final int wordLength = word.length;
+  int pos = contents.indexOf(word);
+  final int contentLength = contents.length;
+  while (pos != -1) {
+    ++count;
+    pos += wordLength;
+    if (pos >= contentLength || count > 100) {
+      break;
+    }
+    pos = contents.indexOf(word, pos);
+  }
+  return count;
+}

e2etests/web/regular_integration_tests/test_driver/treeshaking_e2e_test.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.
+
+import 'package:e2e/e2e_driver.dart' as e2e;
+
+Future<void> main() async => e2e.main();