Close the search by pressing escape (#167648)

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Close
[showSearch()](https://api.flutter.dev/flutter/material/showSearch.html)
by pressing escape button.

feat #148146 


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---------

Co-authored-by: Tong Mu <dkwingsmt@users.noreply.github.com>

packages/flutter/lib/src/material/search.dart

@@ -344,6 +344,15 @@ abstract class SearchDelegate<T> {
       ..pop(result);
   }
 
+  /// Closes the search page and returns to the underlying route whitout result.
+  void _pop(BuildContext context) {
+    _currentBody = null;
+    _focusNode?.unfocus();
+    Navigator.of(context)
+      ..popUntil((Route<dynamic> route) => route == _route)
+      ..pop();
+  }
+
   /// The hint text that is shown in the search field when it is empty.
   ///
   /// If this value is set to null, the value of
@@ -506,7 +515,16 @@ class _SearchPage<T> extends StatefulWidget {
 class _SearchPageState<T> extends State<_SearchPage<T>> {
   // This node is owned, but not hosted by, the search page. Hosting is done by
   // the text field.
-  FocusNode focusNode = FocusNode();
+  late final FocusNode focusNode = FocusNode(
+    onKeyEvent: (FocusNode node, KeyEvent event) {
+      // When the user presses the escape key, close the search page.
+      if (event is KeyDownEvent && event.logicalKey == LogicalKeyboardKey.escape) {
+        widget.delegate._pop(context);
+        return KeyEventResult.handled;
+      }
+      return KeyEventResult.ignored;
+    },
+  );
 
   @override
   void initState() {

packages/flutter/test/material/search_test.dart

@@ -137,6 +137,47 @@ void main() {
     expect(find.text('Suggestions'), findsOneWidget);
   });
 
+  testWidgets('Can close search with escape button and return null', (WidgetTester tester) async {
+    final _TestSearchDelegate delegate = _TestSearchDelegate();
+    addTearDown(() => delegate.dispose());
+    final List<String?> selectedResults = <String?>[];
+
+    await tester.pumpWidget(TestHomePage(delegate: delegate, results: selectedResults));
+
+    // We are on the homepage.
+    expect(find.text('HomeBody'), findsOneWidget);
+    expect(find.text('HomeTitle'), findsOneWidget);
+    expect(find.text('Suggestions'), findsNothing);
+
+    // Open search.
+    await tester.tap(find.byTooltip('Search'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('HomeBody'), findsNothing);
+    expect(find.text('HomeTitle'), findsNothing);
+    expect(find.text('Suggestions'), findsOneWidget);
+    expect(find.text('Bottom'), findsOneWidget);
+
+    // Simulate escape button.
+    await simulateKeyDownEvent(LogicalKeyboardKey.escape, platform: 'windows');
+    await tester.pumpAndSettle();
+
+    expect(selectedResults, <String?>[null]);
+
+    // We are on the homepage again.
+    expect(find.text('HomeBody'), findsOneWidget);
+    expect(find.text('HomeTitle'), findsOneWidget);
+    expect(find.text('Suggestions'), findsNothing);
+
+    // Open search again.
+    await tester.tap(find.byTooltip('Search'));
+    await tester.pumpAndSettle();
+
+    expect(find.text('HomeBody'), findsNothing);
+    expect(find.text('HomeTitle'), findsNothing);
+    expect(find.text('Suggestions'), findsOneWidget);
+  });
+
   testWidgets('Hint text color overridden', (WidgetTester tester) async {
     const String searchHintText = 'Enter search terms';
     final _TestSearchDelegate delegate = _TestSearchDelegate(searchHint: searchHintText);