Create DropdownMenu Widget to Support Material 3 (#116088)

* Created ComboBox

* Fixed failing tests

* Reverted the menu style tests change

* Addressed comments

* Updated documentation and rename foregroundColor variable

* Remamed ComboBox to DropdownMenu

* Removed a unused import

* Removed unused import

Co-authored-by: Qun Cheng <quncheng@google.com>

Author: QuncCccccc

examples/api/lib/material/dropdown_menu/dropdown_menu.0.dart

@@ -0,0 +1,74 @@
+// Copyright 2014 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.
+
+/// Flutter code sample for [DropdownMenu]s. The first dropdown menu has an outlined border
+/// which is the default configuration, and the second one has a filled input decoration.
+
+import 'package:flutter/material.dart';
+
+void main() => runApp(const DropdownMenuExample());
+
+class DropdownMenuExample extends StatelessWidget {
+  const DropdownMenuExample({super.key});
+
+  List<DropdownMenuEntry> getEntryList() {
+    final List<DropdownMenuEntry> entries = <DropdownMenuEntry>[];
+
+    for (int index = 0; index < EntryLabel.values.length; index++) {
+      // Disabled item 1, 2 and 6.
+      final bool enabled = index != 1 && index != 2 && index != 6;
+      entries.add(DropdownMenuEntry(label: EntryLabel.values[index].label, enabled: enabled));
+    }
+    return entries;
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final List<DropdownMenuEntry> dropdownMenuEntries = getEntryList();
+
+    return MaterialApp(
+      theme: ThemeData(
+        useMaterial3: true,
+        colorSchemeSeed: Colors.green
+      ),
+      home: Scaffold(
+        body: SafeArea(
+          child: Padding(
+            padding: const EdgeInsets.only(top: 20),
+            child: Row(
+              mainAxisAlignment: MainAxisAlignment.center,
+              children: <Widget>[
+                DropdownMenu(
+                  label: const Text('Label'),
+                  dropdownMenuEntries: dropdownMenuEntries,
+                ),
+                const SizedBox(width: 20),
+                DropdownMenu(
+                  enableFilter: true,
+                  leadingIcon: const Icon(Icons.search),
+                  label: const Text('Label'),
+                  dropdownMenuEntries: dropdownMenuEntries,
+                  inputDecorationTheme: const InputDecorationTheme(filled: true),
+                )
+              ],
+            ),
+          )
+        ),
+      ),
+    );
+  }
+}
+
+enum EntryLabel {
+  item0('Item 0'),
+  item1('Item 1'),
+  item2('Item 2'),
+  item3('Item 3'),
+  item4('Item 4'),
+  item5('Item 5'),
+  item6('Item 6');
+
+  const EntryLabel(this.label);
+  final String label;
+}

packages/flutter/lib/material.dart

@@ -77,6 +77,8 @@ export 'src/material/drawer.dart';
 export 'src/material/drawer_header.dart';
 export 'src/material/drawer_theme.dart';
 export 'src/material/dropdown.dart';
+export 'src/material/dropdown_menu.dart';
+export 'src/material/dropdown_menu_theme.dart';
 export 'src/material/elevated_button.dart';
 export 'src/material/elevated_button_theme.dart';
 export 'src/material/elevation_overlay.dart';