Migrate to the New Material Buttons (#668)

provider_shopper/lib/screens/cart.dart

@@ -83,12 +83,12 @@ class _CartTotal extends StatelessWidget {
                 builder: (context, cart, child) =>
                     Text('\$${cart.totalPrice}', style: hugeStyle)),
             SizedBox(width: 24),
-            FlatButton(
+            TextButton(
               onPressed: () {
                 Scaffold.of(context).showSnackBar(
                     SnackBar(content: Text('Buying not supported yet.')));
               },
-              color: Colors.white,
+              style: TextButton.styleFrom(primary: Colors.white),
               child: Text('BUY'),
             ),
           ],

provider_shopper/lib/screens/catalog.dart

@@ -43,7 +43,7 @@ class _AddButton extends StatelessWidget {
       (cart) => cart.items.contains(item),
     );
 
-    return FlatButton(
+    return TextButton(
       onPressed: isInCart
           ? null
           : () {
@@ -54,7 +54,14 @@ class _AddButton extends StatelessWidget {
               var cart = context.read<CartModel>();
               cart.add(item);
             },
-      splashColor: Theme.of(context).primaryColor,
+      style: ButtonStyle(
+        overlayColor: MaterialStateProperty.resolveWith<Color>((states) {
+          if (states.contains(MaterialState.pressed)) {
+            return Theme.of(context).primaryColor;
+          }
+          return null; // Defer to the widget's default.
+        }),
+      ),
       child: isInCart ? Icon(Icons.check, semanticLabel: 'ADDED') : Text('ADD'),
     );
   }

provider_shopper/lib/screens/login.dart

@@ -32,12 +32,14 @@ class MyLogin extends StatelessWidget {
               SizedBox(
                 height: 24,
               ),
-              RaisedButton(
-                color: Colors.yellow,
+              ElevatedButton(
                 child: Text('ENTER'),
                 onPressed: () {
                   Navigator.pushReplacementNamed(context, '/catalog');
                 },
+                style: ElevatedButton.styleFrom(
+                  primary: Colors.yellow,
+                ),
               )
             ],
           ),

provider_shopper/test/catalog_widget_test.dart

@@ -48,7 +48,7 @@ void main() {
       expect(find.text('ADD'), findsWidgets);
 
       // Performing the click on the ADD button of the first item in the list.
-      await tester.tap(find.widgetWithText(FlatButton, 'ADD').first);
+      await tester.tap(find.widgetWithText(TextButton, 'ADD').first);
       await tester.pumpAndSettle();
 
       // Verifying if the tapped ADD button has changed to the check icon.