Make UserAccountsDrawerHeader accessible (#13851)

Fixes #13743 
Fixes #12379
Follow-up to #13745

Also adds an option to hide gestures introduced by `InkWell` and `InkResponse` from the semantics tree (see also `GestureDetector.excludeFromSemantics`).

examples/flutter_gallery/lib/demo/material/drawer_demo.dart

@@ -100,17 +100,33 @@ class _DrawerDemoState extends State<DrawerDemo> with TickerProviderStateMixin {
                   package: _kGalleryAssetsPackage,
                 ),
               ),
-              otherAccountsPictures: const <Widget>[
-                const CircleAvatar(
-                  backgroundImage: const AssetImage(
-                    _kAsset1,
-                    package: _kGalleryAssetsPackage,
+              otherAccountsPictures:  <Widget>[
+                new GestureDetector(
+                  onTap: () {
+                    _onOtherAccountsTap(context);
+                  },
+                  child: new Semantics(
+                    label: 'Switch to Account B',
+                    child: const CircleAvatar(
+                      backgroundImage: const AssetImage(
+                        _kAsset1,
+                        package: _kGalleryAssetsPackage,
+                      ),
+                    ),
                   ),
                 ),
-                const CircleAvatar(
-                  backgroundImage: const AssetImage(
-                    _kAsset2,
-                    package: _kGalleryAssetsPackage,
+                new GestureDetector(
+                  onTap: () {
+                    _onOtherAccountsTap(context);
+                  },
+                  child: new Semantics(
+                    label: 'Switch to Account C',
+                    child: const CircleAvatar(
+                      backgroundImage: const AssetImage(
+                        _kAsset2,
+                        package: _kGalleryAssetsPackage,
+                      ),
+                    ),
                   ),
                 ),
               ],
@@ -213,4 +229,21 @@ class _DrawerDemoState extends State<DrawerDemo> with TickerProviderStateMixin {
       ),
     );
   }
+
+  void _onOtherAccountsTap(BuildContext context) {
+    showDialog<Null>(
+      context: context,
+      child: new AlertDialog(
+        title: const Text('Account switching not implemented.'),
+        actions: <Widget>[
+          new FlatButton(
+            child: const Text('OK'),
+            onPressed: () {
+              Navigator.of(context).pop();
+            },
+          ),
+        ],
+      ),
+    );
+  }
 }

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

@@ -96,6 +96,7 @@ class InkResponse extends StatefulWidget {
     this.highlightColor,
     this.splashColor,
     this.enableFeedback: true,
+    this.excludeFromSemantics: false,
   }) : assert(enableFeedback != null), super(key: key);
 
   /// The widget below this widget in the tree.
@@ -194,6 +195,15 @@ class InkResponse extends StatefulWidget {
   ///  * [Feedback] for providing platform-specific feedback to certain actions.
   final bool enableFeedback;
 
+  /// Whether to exclude the gestures introduced by this widget from the
+  /// semantics tree.
+  ///
+  /// For example, a long-press gesture for showing a tooltip is usually
+  /// excluded because the tooltip itself is included in the semantics
+  /// tree directly and so having a gesture to show it would result in
+  /// duplication of information.
+  final bool excludeFromSemantics;
+
   /// The rectangle to use for the highlight effect and for clipping
   /// the splash effects if [containedInkWell] is true.
   ///
@@ -379,7 +389,8 @@ class _InkResponseState<T extends InkResponse> extends State<T> with AutomaticKe
       onDoubleTap: widget.onDoubleTap != null ? _handleDoubleTap : null,
       onLongPress: widget.onLongPress != null ? () => _handleLongPress(context) : null,
       behavior: HitTestBehavior.opaque,
-      child: widget.child
+      child: widget.child,
+      excludeFromSemantics: widget.excludeFromSemantics,
     );
   }
 
@@ -427,6 +438,7 @@ class InkWell extends InkResponse {
     Color splashColor,
     BorderRadius borderRadius,
     bool enableFeedback: true,
+    bool excludeFromSemantics: false,
   }) : super(
     key: key,
     child: child,
@@ -440,5 +452,6 @@ class InkWell extends InkResponse {
     splashColor: splashColor,
     borderRadius: borderRadius,
     enableFeedback: enableFeedback,
+    excludeFromSemantics: excludeFromSemantics,
   );
 }

packages/flutter/test/material/ink_well_test.dart

@@ -7,6 +7,7 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 import '../rendering/mock_canvas.dart';
+import '../widgets/semantics_tester.dart';
 import 'feedback_tester.dart';
 
 void main() {
@@ -156,4 +157,33 @@ void main() {
     await runTest(true);
     await runTest(false);
   });
+
+  testWidgets('excludeFromSemantics', (WidgetTester tester) async {
+    final SemanticsTester semantics = new SemanticsTester(tester);
+
+    await tester.pumpWidget(new Directionality(
+      textDirection: TextDirection.ltr,
+      child: new Material(
+        child: new InkWell(
+          onTap: () { },
+          child: const Text('Button'),
+        ),
+      ),
+    ));
+    expect(semantics, includesNodeWith(label: 'Button', actions: <SemanticsAction>[SemanticsAction.tap]));
+
+    await tester.pumpWidget(new Directionality(
+      textDirection: TextDirection.ltr,
+      child: new Material(
+        child: new InkWell(
+          onTap: () { },
+          child: const Text('Button'),
+          excludeFromSemantics: true,
+        ),
+      ),
+    ));
+    expect(semantics, isNot(includesNodeWith(label: 'Button', actions: <SemanticsAction>[SemanticsAction.tap])));
+
+    semantics.dispose();
+  });
 }