[ExpansionTile] Adds tilePadding property to ExpansionTile (#55221)

* Adds tilePadding property to ExpansionTile

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

@@ -41,6 +41,7 @@ class ExpansionTile extends StatefulWidget {
     this.children = const <Widget>[],
     this.trailing,
     this.initiallyExpanded = false,
+    this.tilePadding,
   }) : assert(initiallyExpanded != null),
        super(key: key);
 
@@ -80,6 +81,15 @@ class ExpansionTile extends StatefulWidget {
   /// Specifies if the list tile is initially expanded (true) or collapsed (false, the default).
   final bool initiallyExpanded;
 
+  /// Specifies padding for the [ListTile].
+  ///
+  /// Analogous to [ListTile.contentPadding], this property defines the insets for
+  /// the [leading], [title], [subtitle] and [trailing] widgets. It does not inset
+  /// the expanded [children] widgets.
+  ///
+  /// When the value is null, the tile's padding is `EdgeInsets.symmetric(horizontal: 16.0)`.
+  final EdgeInsetsGeometry tilePadding;
+
   @override
   _ExpansionTileState createState() => _ExpansionTileState();
 }
@@ -165,6 +175,7 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
             textColor: _headerColor.value,
             child: ListTile(
               onTap: _handleTap,
+              contentPadding: widget.tilePadding,
               leading: widget.leading,
               title: widget.title,
               subtitle: widget.subtitle,

packages/flutter/test/material/expansion_tile_test.dart

@@ -229,4 +229,31 @@ void main() {
 
     expect(find.text('Subtitle'), findsOneWidget);
   });
+
+  testWidgets('ExpansionTile padding test', (WidgetTester tester) async {
+    await tester.pumpWidget(const MaterialApp(
+      home: Material(
+        child: Center(
+          child: ExpansionTile(
+            title: Text('Hello'),
+            tilePadding: EdgeInsets.fromLTRB(8, 12, 4, 10),
+          ),
+        ),
+      ),
+    ));
+
+    final Rect titleRect = tester.getRect(find.text('Hello'));
+    final Rect trailingRect = tester.getRect(find.byIcon(Icons.expand_more));
+    final Rect listTileRect = tester.getRect(find.byType(ListTile));
+    final Rect tallerWidget = titleRect.height > trailingRect.height ? titleRect : trailingRect;
+
+    // Check the positions of title and trailing Widgets, after padding is applied.
+    expect(listTileRect.left, titleRect.left - 8);
+    expect(listTileRect.right, trailingRect.right + 4);
+
+    // Calculate the remaining height of ListTile from the default height.
+    final double remainingHeight = 56 - tallerWidget.height;
+    expect(listTileRect.top, tallerWidget.top - remainingHeight / 2 - 12);
+    expect(listTileRect.bottom, tallerWidget.bottom + remainingHeight / 2 + 10);
+  });
 }