Change PopupMenuButton.icon type to Widget (#43526)

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

@@ -978,11 +978,13 @@ class PopupMenuButton<T> extends StatefulWidget {
   /// to set the padding to zero.
   final EdgeInsetsGeometry padding;
 
-  /// If provided, the widget used for this button.
+  /// If provided, [child] is the widget used for this button
+  /// and the button will utilize an [InkWell] for taps.
   final Widget child;
 
-  /// If provided, the icon used for this button.
-  final Icon icon;
+  /// If provided, the [icon] is used for this button
+  /// and the button will behave like an [IconButton].
+  final Widget icon;
 
   /// The offset applied to the Popup Menu Button.
   ///

packages/flutter/test/material/popup_menu_test.dart

@@ -974,6 +974,29 @@ void main() {
     expect(find.byType(Tooltip), findsNWidgets(3));
     expect(find.byTooltip('Test tooltip',), findsNWidgets(3));
   });
+
+  testWidgets('Allow Widget for PopupMenuButton.icon', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Material(
+          child: PopupMenuButton<int>(
+            itemBuilder: (BuildContext context) {
+              return <PopupMenuEntry<int>>[
+                const PopupMenuItem<int>(
+                  value: 1,
+                  child: Text('Tap me please!'),
+                ),
+              ];
+            },
+            tooltip: 'Test tooltip',
+            icon: const Text('PopupMenuButton icon'),
+          ),
+        ),
+      ),
+    );
+
+    expect(find.text('PopupMenuButton icon'), findsOneWidget);
+  });
 }
 
 class TestApp extends StatefulWidget {