Switch DatePicker to SliverGrid (#7890)

After this patch, the old grid code is not used in the framework.

packages/flutter/lib/src/widgets/sliver.dart

@@ -79,8 +79,20 @@ class SliverChildBuilderDelegate extends SliverChildDelegate {
 // /// demand). For example, the body of a dialog box might fit both of these
 // /// conditions.
 class SliverChildListDelegate extends SliverChildDelegate {
-  const SliverChildListDelegate(this.children);
+  const SliverChildListDelegate(this.children, { this.addRepaintBoundaries: true });
 
+  /// Whether to wrap each child in a [RepaintBoundary].
+  ///
+  /// Typically, children in a scrolling container are wrapped in repaint
+  /// boundaries so that they do not need to be repainted as the list scrolls.
+  /// If the children are easy to repaint (e.g., solid color blocks or a short
+  /// snippet of text), it might be more efficient to not add a repaint boundary
+  /// and simply repaint the children during scrolling.
+  ///
+  /// Defaults to true.
+  final bool addRepaintBoundaries;
+
+  /// The widgets to display.
   final List<Widget> children;
 
   @override
@@ -90,7 +102,7 @@ class SliverChildListDelegate extends SliverChildDelegate {
       return null;
     final Widget child = children[index];
     assert(child != null);
-    return new RepaintBoundary.wrap(child, index);
+    return addRepaintBoundaries ? new RepaintBoundary.wrap(child, index) : child;
   }
 
   @override

packages/flutter/test/material/date_picker_test.dart

@@ -41,16 +41,16 @@ void main() {
                           setState(() {
                             _selectedDate = value;
                           });
-                        }
-                      )
-                    )
-                  )
+                        },
+                      ),
+                    ),
+                  ),
                 );
-              }
-            )
-          )
-        ]
-      )
+              },
+            ),
+          ),
+        ],
+      ),
     );
 
     await tester.tapAt(const Point(50.0, 100.0));
@@ -79,7 +79,7 @@ void main() {
     expect(_selectedDate, equals(new DateTime(2016, DateTime.SEPTEMBER, 25)));
     await tester.pump(const Duration(seconds: 2));
 
-    await tester.scroll(find.byKey(_datePickerKey), const Offset(300.0, 10.0));
+    await tester.scroll(find.byKey(_datePickerKey), const Offset(300.0, 0.0));
     await tester.pump();
     await tester.pump(const Duration(seconds: 2));
     expect(_selectedDate, equals(new DateTime(2016, DateTime.SEPTEMBER, 25)));
@@ -105,17 +105,17 @@ void main() {
                           firstDate: new DateTime(0),
                           lastDate: new DateTime(9999),
                           onChanged: (DateTime value) { },
-                          selectedDate: new DateTime(2000, DateTime.JANUARY, 1)
-                        )
-                      )
-                    )
-                  )
+                          selectedDate: new DateTime(2000, DateTime.JANUARY, 1),
+                        ),
+                      ),
+                    ),
+                  ),
                 );
-              }
-            )
-          )
-        ]
-      )
+              },
+            ),
+          ),
+        ],
+      ),
     );
     await tester.pump(const Duration(seconds: 5));
   });