Update an IconButton sample, add RaisedButton sample (#27169)

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

@@ -47,11 +47,25 @@ const double _kMinButtonSize = 48.0;
 /// ```
 ///
 /// ```dart
-/// Widget build(BuildContext) {
-///   return IconButton(
+/// Widget build(BuildContext context) {
+///   return Scaffold(
+///     body: Center(
+///       child: Column(
+///         mainAxisSize: MainAxisSize.min,
+///         children: <Widget>[
+///           IconButton(
 ///             icon: Icon(Icons.volume_up),
-///     tooltip: 'Increase volume by 10%',
-///     onPressed: () { setState(() { _volume *= 1.1; }); },
+///             tooltip: 'Increase volume by 10',
+///             onPressed: () {
+///               setState(() {
+///                 _volume += 10;
+///               });
+///             },
+///           ),
+///           Text('Volume : $_volume')
+///         ],
+///       ),
+///     ),
 ///   );
 /// }
 /// ```

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

@@ -31,6 +31,46 @@ import 'theme_data.dart';
 /// Raised buttons have a minimum size of 88.0 by 36.0 which can be overidden
 /// with [ButtonTheme].
 ///
+/// {@tool snippet --template=stateless_widget}
+///
+/// This sample shows how to render a disabled RaisedButton, an enabled RaisedButton
+/// and lastly a RaisedButton with gradient background.
+///
+/// ```dart
+/// Scaffold(
+///   body: Center(
+///     child: Column(
+///       mainAxisSize: MainAxisSize.min,
+///       children: <Widget>[
+///         RaisedButton(
+///           onPressed: null,
+///           child: const Text('Disabled Button'),
+///         ),
+///         RaisedButton(
+///           onPressed: () {},
+///           child: const Text('Enabled Button'),
+///         ),
+///         RaisedButton(
+///           onPressed: () {},
+///           textColor: Colors.white,
+///           padding: const EdgeInsets.all(0.0),
+///           child: Container(
+///             decoration: const BoxDecoration(
+///               gradient: LinearGradient(
+///                 colors: <Color>[Colors.red, Colors.green, Colors.blue],
+///               ),
+///             ),
+///             padding: const EdgeInsets.all(10.0),
+///             child: Text('Gradient Button'),
+///           ),
+///         ),
+///       ],
+///     ),
+///   ),
+/// )
+/// ```
+/// {@end-tool}
+///
 /// See also:
 ///
 ///  * [FlatButton], a material design button without a shadow.