Accessibility fixes for new gallery (#16973)

examples/flutter_gallery/lib/gallery/backdrop.dart

diff --git a/examples/flutter_gallery/lib/gallery/backdrop.dart b/examples/flutter_gallery/lib/gallery/backdrop.dart
index 205ab26..0c70c96 100644
--- a/examples/flutter_gallery/lib/gallery/backdrop.dart
+++ b/examples/flutter_gallery/lib/gallery/backdrop.dart
@@ -46,7 +46,7 @@
   void initState() {
     super.initState();
     widget.controller.addStatusListener(_handleStatusChange);
-    _ignoring = widget.controller.status != AnimationStatus.completed;
+    _ignoring = widget.controller.status != widget.status;
   }
 
   @override
@@ -283,7 +283,7 @@
               ),
               trailing: new IconButton(
                 onPressed: _toggleFrontLayer,
-                tooltip: 'Show options page',
+                tooltip: 'Toggle options page',
                 icon: new AnimatedIcon(
                   icon: AnimatedIcons.close_menu,
                   progress: _controller,
@@ -328,14 +328,16 @@
         ),
         new PositionedTransition(
           rect: frontRelativeRect,
-          child: new Container(
-            alignment: Alignment.topLeft,
-            child: new GestureDetector(
-              behavior: HitTestBehavior.opaque,
-              onTap: _toggleFrontLayer,
-              onVerticalDragUpdate: _handleDragUpdate,
-              onVerticalDragEnd: _handleDragEnd,
-              child: widget.frontHeading,
+          child: new ExcludeSemantics(
+            child: new Container(
+              alignment: Alignment.topLeft,
+              child: new GestureDetector(
+                behavior: HitTestBehavior.opaque,
+                onTap: _toggleFrontLayer,
+                onVerticalDragUpdate: _handleDragUpdate,
+                onVerticalDragEnd: _handleDragEnd,
+                child: widget.frontHeading,
+              ),
             ),
           ),
         ),

examples/flutter_gallery/lib/gallery/options.dart

diff --git a/examples/flutter_gallery/lib/gallery/options.dart b/examples/flutter_gallery/lib/gallery/options.dart
index f3fbe02..7f9064c 100644
--- a/examples/flutter_gallery/lib/gallery/options.dart
+++ b/examples/flutter_gallery/lib/gallery/options.dart
@@ -96,17 +96,19 @@
   Widget build(BuildContext context) {
     final double textScaleFactor = MediaQuery.of(context)?.textScaleFactor ?? 1.0;
 
-    return new Container(
-      constraints: new BoxConstraints(minHeight: _kItemHeight * textScaleFactor),
-      padding: _kItemPadding,
-      alignment: AlignmentDirectional.centerStart,
-      child: new DefaultTextStyle(
-        style: DefaultTextStyle.of(context).style,
-        maxLines: 2,
-        overflow: TextOverflow.fade,
-        child: new IconTheme(
-          data: Theme.of(context).primaryIconTheme,
-          child: child,
+    return new MergeSemantics(
+      child: new Container(
+        constraints: new BoxConstraints(minHeight: _kItemHeight * textScaleFactor),
+        padding: _kItemPadding,
+        alignment: AlignmentDirectional.centerStart,
+        child: new DefaultTextStyle(
+          style: DefaultTextStyle.of(context).style,
+          maxLines: 2,
+          overflow: TextOverflow.fade,
+          child: new IconTheme(
+            data: Theme.of(context).primaryIconTheme,
+            child: child,
+          ),
         ),
       ),
     );

examples/flutter_gallery/test/drawer_test.dart

diff --git a/examples/flutter_gallery/test/drawer_test.dart b/examples/flutter_gallery/test/drawer_test.dart
index bcc1203..1315a43 100644
--- a/examples/flutter_gallery/test/drawer_test.dart
+++ b/examples/flutter_gallery/test/drawer_test.dart
@@ -26,7 +26,7 @@
     await tester.pump(); // triggers a frame
 
     // Show the options page
-    await tester.tap(find.byTooltip('Show options page'));
+    await tester.tap(find.byTooltip('Toggle options page'));
     await tester.pumpAndSettle();
 
     MaterialApp app = find.byType(MaterialApp).evaluate().first.widget;
@@ -89,7 +89,7 @@
     expect(hasFeedback, true);
 
     // Hide the options page
-    await tester.tap(find.byTooltip('Show options page'));
+    await tester.tap(find.byTooltip('Toggle options page'));
     await tester.pumpAndSettle();
   });
 }

examples/flutter_gallery/test/simple_smoke_test.dart

diff --git a/examples/flutter_gallery/test/simple_smoke_test.dart b/examples/flutter_gallery/test/simple_smoke_test.dart
index 21baf51..553cdac 100644
--- a/examples/flutter_gallery/test/simple_smoke_test.dart
+++ b/examples/flutter_gallery/test/simple_smoke_test.dart
@@ -16,7 +16,7 @@
     await tester.pump(); // see https://github.com/flutter/flutter/issues/1865
     await tester.pump(); // triggers a frame
 
-    final Finder showOptionsPageButton = find.byTooltip('Show options page');
+    final Finder showOptionsPageButton = find.byTooltip('Toggle options page');
 
     // Show the options page
     await tester.tap(showOptionsPageButton);

examples/flutter_gallery/test/smoke_test.dart

diff --git a/examples/flutter_gallery/test/smoke_test.dart b/examples/flutter_gallery/test/smoke_test.dart
index 1b50073..82636ba 100644
--- a/examples/flutter_gallery/test/smoke_test.dart
+++ b/examples/flutter_gallery/test/smoke_test.dart
@@ -96,7 +96,7 @@
 }
 
 Future<Null> smokeOptionsPage(WidgetTester tester) async {
-  final Finder showOptionsPageButton = find.byTooltip('Show options page');
+  final Finder showOptionsPageButton = find.byTooltip('Toggle options page');
 
   // Show the options page
   await tester.tap(showOptionsPageButton);