Add a property to Material icon button to customize the splash radius (#55761)

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

@@ -142,6 +142,7 @@ class IconButton extends StatelessWidget {
     this.visualDensity,
     this.padding = const EdgeInsets.all(8.0),
     this.alignment = Alignment.center,
+    this.splashRadius,
     @required this.icon,
     this.color,
     this.focusColor,
@@ -158,6 +159,7 @@ class IconButton extends StatelessWidget {
   }) : assert(iconSize != null),
        assert(padding != null),
        assert(alignment != null),
+       assert(splashRadius == null || splashRadius > 0),
        assert(autofocus != null),
        assert(icon != null),
        super(key: key);
@@ -202,6 +204,11 @@ class IconButton extends StatelessWidget {
   ///    relative to text direction.
   final AlignmentGeometry alignment;
 
+  /// The splash radius.
+  ///
+  /// If null, default splash radius of [Material.defaultSplashRadius] is used.
+  final double splashRadius;
+
   /// The icon to display inside the button.
   ///
   /// The [Icon.size] and [Icon.color] of the icon is configured automatically
@@ -369,7 +376,7 @@ class IconButton extends StatelessWidget {
         hoverColor: hoverColor ?? Theme.of(context).hoverColor,
         highlightColor: highlightColor ?? Theme.of(context).highlightColor,
         splashColor: splashColor ?? Theme.of(context).splashColor,
-        radius: math.max(
+        radius: splashRadius ?? math.max(
           Material.defaultSplashRadius,
           (iconSize + math.min(padding.horizontal, padding.vertical)) * 0.7,
           // x 0.5 for diameter -> radius and + 40% overflow derived from other Material apps.

packages/flutter/test/material/icon_button_test.dart

@@ -337,6 +337,37 @@ void main() {
     await gesture.up();
   });
 
+  testWidgets('IconButton with explicit splash radius',
+      (WidgetTester tester) async {
+    const double splashRadius = 30.0;
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Material(
+          child: Center(
+            child: IconButton(
+              icon: const Icon(Icons.android),
+              splashRadius: splashRadius,
+              onPressed: () { /* enable the button */ },
+            ),
+          ),
+        ),
+      ),
+    );
+
+    final Offset center = tester.getCenter(find.byType(IconButton));
+    final TestGesture gesture = await tester.startGesture(center);
+    await tester.pump(); // Start gesture.
+    await tester.pump(const Duration(milliseconds: 1000)); // Wait for splash to be well under way.
+
+    expect(
+      Material.of(tester.element(find.byType(IconButton))),
+      paints
+        ..circle(radius: splashRadius)
+    );
+
+    await gesture.up();
+  });
+
   testWidgets('IconButton Semantics (enabled)', (WidgetTester tester) async {
     final SemanticsTester semantics = SemanticsTester(tester);