Provide a way to change the default PopupMenuButton's icon size (#68000)

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

@@ -949,6 +949,7 @@ class PopupMenuButton<T> extends StatefulWidget {
     this.padding = const EdgeInsets.all(8.0),
     this.child,
     this.icon,
+    this.iconSize,
     this.offset = Offset.zero,
     this.enabled = true,
     this.shape,
@@ -1048,6 +1049,11 @@ class PopupMenuButton<T> extends StatefulWidget {
   ///  * [Feedback] for providing platform-specific feedback to certain actions.
   final bool? enableFeedback;
 
+  /// If provided, the size of the [Icon].
+  ///
+  /// If this property is null, the default size is 24.0 pixels.
+  final double? iconSize;
+
   @override
   PopupMenuButtonState<T> createState() => PopupMenuButtonState<T>();
 }
@@ -1134,6 +1140,7 @@ class PopupMenuButtonState<T> extends State<PopupMenuButton<T>> {
     return IconButton(
       icon: widget.icon ?? Icon(Icons.adaptive.more),
       padding: widget.padding,
+      iconSize: widget.iconSize ?? 24.0,
       tooltip: widget.tooltip ?? MaterialLocalizations.of(context).showMenuTooltip,
       onPressed: widget.enabled ? showButtonMenu : null,
       enableFeedback: enableFeedback,

packages/flutter/test/material/popup_menu_test.dart

@@ -1876,6 +1876,34 @@ void main() {
       expect(feedback.hapticCount, 0);
     });
   });
+
+  testWidgets('iconSize parameter tests', (WidgetTester tester) async {
+    Future<void> buildFrame({double? iconSize}) {
+      return tester.pumpWidget(
+        MaterialApp(
+          home: Scaffold(
+            body: Center(
+              child: PopupMenuButton<String>(
+                iconSize: iconSize,
+                itemBuilder: (_) => <PopupMenuEntry<String>>[
+                  const PopupMenuItem<String>(
+                    value: 'value',
+                    child: Text('child'),
+                  ),
+                ],
+              ),
+            ),
+          ),
+        ),
+      );
+    }
+
+    await buildFrame();
+    expect(tester.widget<IconButton>(find.byType(IconButton)).iconSize, 24);
+
+    await buildFrame(iconSize: 50);
+    expect(tester.widget<IconButton>(find.byType(IconButton)).iconSize, 50);
+  });
 }
 
 class TestApp extends StatefulWidget {