Feature: `ExpandIcon` should use the `size` parameter (#45712)

* ExpandIcon should use the size parameter

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

diff --git a/packages/flutter/lib/src/material/expand_icon.dart b/packages/flutter/lib/src/material/expand_icon.dart
index 5e5729b..cc3fc51 100644
--- a/packages/flutter/lib/src/material/expand_icon.dart
+++ b/packages/flutter/lib/src/material/expand_icon.dart
@@ -177,6 +177,7 @@
       onTapHint: widget.onPressed == null ? null : onTapHint,
       child: IconButton(
         padding: widget.padding,
+        iconSize: widget.size,
         color: _iconColor,
         disabledColor: widget.disabledColor,
         onPressed: widget.onPressed == null ? null : _handlePressed,

packages/flutter/test/material/expand_icon_test.dart

diff --git a/packages/flutter/test/material/expand_icon_test.dart b/packages/flutter/test/material/expand_icon_test.dart
index 5ef6c32..30fd8d8 100644
--- a/packages/flutter/test/material/expand_icon_test.dart
+++ b/packages/flutter/test/material/expand_icon_test.dart
@@ -134,6 +134,45 @@
     expect(rotation.turns.value, 0.5);
   });
 
+  testWidgets('ExpandIcon default size is 24', (WidgetTester tester) async {
+    final ExpandIcon expandIcon =  ExpandIcon(
+      onPressed: (bool isExpanded) {},
+    );
+
+    await tester.pumpWidget(wrap(
+      child: expandIcon
+    ));
+
+    final ExpandIcon icon = tester.firstWidget(find.byWidget(expandIcon));
+    expect(icon.size, 24);
+  });
+
+  testWidgets('ExpandIcon has the correct given size', (WidgetTester tester) async {
+    ExpandIcon expandIcon =  ExpandIcon(
+      size: 36,
+      onPressed: (bool isExpanded) {},
+    );
+
+    await tester.pumpWidget(wrap(
+      child: expandIcon
+    ));
+
+    ExpandIcon icon = tester.firstWidget(find.byWidget(expandIcon));
+    expect(icon.size, 36);
+
+    expandIcon =  ExpandIcon(
+      size: 48,
+      onPressed: (bool isExpanded) {},
+    );
+
+    await tester.pumpWidget(wrap(
+      child: expandIcon
+    ));
+
+    icon = tester.firstWidget(find.byWidget(expandIcon));
+    expect(icon.size, 48);
+  });
+
   testWidgets('ExpandIcon has correct semantic hints', (WidgetTester tester) async {
     final SemanticsHandle handle = tester.ensureSemantics();
     const DefaultMaterialLocalizations localizations = DefaultMaterialLocalizations();