Apply @required according to the rules, for all of material/* (#7732)

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

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 
 import 'colors.dart';
@@ -42,8 +43,8 @@ class Chip extends StatelessWidget {
   const Chip({
     Key key,
     this.avatar,
-    this.label,
-    this.onDeleted
+    @required this.label,
+    this.onDeleted,
   }) : super(key: key);
 
   /// A widget to display prior to the chip's label.

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

@@ -4,6 +4,7 @@
 
 import 'dart:math' as math;
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 
@@ -34,7 +35,7 @@ class DataColumn {
   ///
   /// The [label] argument must not be null.
   const DataColumn({
-    this.label,
+    @required this.label,
     this.tooltip,
     this.numeric: false,
     this.onSort

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

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 
 import 'debug.dart';
@@ -35,7 +36,7 @@ class DrawerHeader extends StatelessWidget {
     this.padding: const EdgeInsets.fromLTRB(16.0, 16.0, 16.0, 8.0),
     this.duration: const Duration(milliseconds: 250),
     this.curve: Curves.fastOutSlowIn,
-    this.child
+    @required this.child,
   }) : super(key: key);
 
   /// Decoration for the main drawer header [Container]; useful for applying
@@ -61,6 +62,9 @@ class DrawerHeader extends StatelessWidget {
   final Curve curve;
 
   /// A widget to be placed inside the drawer header, inset by the [padding].
+  ///
+  /// This widget will be sized to the size of the header. To position the child
+  /// precisely, consider using an [Align] or [Center] widget.
   final Widget child;
 
   @override

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

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 
 import 'colors.dart';
@@ -33,7 +34,7 @@ class DrawerItem extends StatelessWidget {
   const DrawerItem({
     Key key,
     this.icon: const Icon(null),
-    this.child,
+    @required this.child,
     this.onPressed,
     this.selected: false
   }) : super(key: key);

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

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 
 /// A tile in a material design grid list.
@@ -19,7 +20,7 @@ class GridTile extends StatelessWidget {
   /// Creates a grid tile.
   ///
   /// Must have a child. Does not typically have both a header and a footer.
-  GridTile({ Key key, this.header, this.footer, this.child }) : super(key: key) {
+  GridTile({ Key key, this.header, this.footer, @required this.child }) : super(key: key) {
     assert(child != null);
   }
 

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

@@ -237,6 +237,7 @@ class InputContainer extends StatefulWidget {
   /// Defaults to true.
   final bool showDivider;
 
+  /// The widget below this widget in the tree.
   final Widget child;
 
   @override

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

@@ -35,7 +35,7 @@ class MaterialSlice extends MergeableMaterialItem {
   /// [MergeableMaterial].
   MaterialSlice({
     @required LocalKey key,
-    this.child
+    @required this.child,
   }) : super(key) {
     assert(key != null);
   }

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

@@ -7,6 +7,7 @@
 import 'dart:async' show Timer;
 import 'dart:math' as math;
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 
 import 'theme.dart';
@@ -100,7 +101,7 @@ class OverscrollIndicator extends StatefulWidget {
     Key key,
     this.scrollableKey,
     this.edge: ScrollableEdge.both,
-    this.child
+    @required this.child,
   }) : super(key: key) {
     assert(child != null);
     assert(edge != null);

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

@@ -20,7 +20,7 @@ class _MountainViewPageTransition extends AnimatedWidget {
   _MountainViewPageTransition({
     Key key,
     Animation<double> animation,
-    this.child
+    this.child,
   }) : super(
     key: key,
     animation: _kTween.animate(new CurvedAnimation(

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

@@ -115,7 +115,7 @@ class PopupMenuItem<T> extends PopupMenuEntry<T> {
     Key key,
     this.value,
     this.enabled: true,
-    this.child
+    @required this.child,
   }) : super(key: key);
 
   @override

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

@@ -132,7 +132,7 @@ class RaisedButton extends StatelessWidget {
       elevation: enabled ? elevation : disabledElevation,
       highlightElevation: enabled ? highlightElevation : disabledElevation,
       colorBrightness: colorBrightness,
-      child: child
+      child: child,
     );
   }
 }

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

@@ -172,7 +172,7 @@ class _ScaffoldLayout extends MultiChildLayoutDelegate {
 class _FloatingActionButtonTransition extends StatefulWidget {
   _FloatingActionButtonTransition({
     Key key,
-    this.child
+    this.child,
   }) : super(key: key);
 
   final Widget child;
@@ -266,7 +266,7 @@ class _FloatingActionButtonTransitionState extends State<_FloatingActionButtonTr
     if (_previousAnimation.status != AnimationStatus.dismissed) {
       children.add(new ScaleTransition(
         scale: _previousAnimation,
-        child: _previousChild
+        child: _previousChild,
       ));
     }
     if (_currentAnimation.status != AnimationStatus.dismissed) {
@@ -274,7 +274,7 @@ class _FloatingActionButtonTransitionState extends State<_FloatingActionButtonTr
         scale: _currentAnimation,
         child: new RotationTransition(
           turns: _kFloatingActionButtonTurnTween.animate(_currentAnimation),
-          child: config.child
+          child: config.child,
         )
       ));
     }

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

@@ -147,11 +147,11 @@ class SnackBar extends StatelessWidget {
   /// The [content] argument must be non-null.
   SnackBar({
     Key key,
-    this.content,
+    @required this.content,
     this.backgroundColor,
     this.action,
     this.duration: _kSnackBarDisplayDuration,
-    this.animation
+    this.animation,
   }) : super(key: key) {
     assert(content != null);
   }
@@ -203,7 +203,7 @@ class SnackBar extends StatelessWidget {
           padding: const EdgeInsets.symmetric(vertical: _kSingleLineVerticalPadding),
           child: new DefaultTextStyle(
             style: darkTheme.textTheme.subhead,
-            child: content
+            child: content,
           )
         )
       )

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

@@ -144,7 +144,7 @@ class DefaultTabController extends StatefulWidget {
     Key key,
     @required this.length,
     this.initialIndex: 0,
-    this.child
+    @required this.child,
   }) : super(key: key);
 
   /// The total number of tabs. Must be greater than one.

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

@@ -109,7 +109,7 @@ class _TabStyle extends AnimatedWidget {
     this.selected,
     this.labelColor,
     this.unselectedLabelColor,
-    this.child
+    @required this.child,
   }) : super(key: key, animation: animation);
 
   final bool selected;

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

@@ -160,7 +160,7 @@ class AnimatedTheme extends ImplicitlyAnimatedWidget {
     this.isMaterialAppTheme: false,
     Curve curve: Curves.linear,
     Duration duration: kThemeAnimationDuration,
-    this.child
+    @required this.child,
   }) : super(key: key, curve: curve, duration: duration) {
     assert(child != null);
     assert(data != null);

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

@@ -47,7 +47,7 @@ class Tooltip extends StatefulWidget {
     this.padding: const EdgeInsets.symmetric(horizontal: 16.0),
     this.verticalOffset: 24.0,
     this.preferBelow: true,
-    this.child
+    this.child,
   }) : super(key: key) {
     assert(message != null);
     assert(height != null);
@@ -181,7 +181,7 @@ class _TooltipState extends State<Tooltip> with SingleTickerProviderStateMixin {
       excludeFromSemantics: true,
       child: new Semantics(
         label: config.message,
-        child: config.child
+        child: config.child,
       )
     );
   }

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

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
 import 'debug.dart';
@@ -50,8 +51,8 @@ class _AccountPictures extends StatelessWidget {
 class _AccountDetails extends StatelessWidget {
   _AccountDetails({
     Key key,
-    this.accountName,
-    this.accountEmail,
+    @required this.accountName,
+    @required this.accountEmail,
     this.onTap,
     this.isOpen,
   }) : super(key: key);
@@ -136,8 +137,8 @@ class UserAccountsDrawerHeader extends StatefulWidget {
     this.decoration,
     this.currentAccountPicture,
     this.otherAccountsPictures,
-    this.accountName,
-    this.accountEmail,
+    @required this.accountName,
+    @required this.accountEmail,
     this.onDetailsPressed
   }) : super(key: key);