Remove the 'demo' wording from gallery (#15640)

examples/flutter_gallery/lib/gallery/item.dart

@@ -55,28 +55,28 @@ List<GalleryItem> _buildGalleryItems() {
     new GalleryItem(
       title: 'Shrine',
       subtitle: 'Basic shopping app',
-      category: 'Demos',
+      category: 'Vignettes',
       routeName: ShrineDemo.routeName,
       buildRoute: (BuildContext context) => new ShrineDemo(),
     ),
     new GalleryItem(
       title: 'Contact profile',
       subtitle: 'Address book entry with a flexible appbar',
-      category: 'Demos',
+      category: 'Vignettes',
       routeName: ContactsDemo.routeName,
       buildRoute: (BuildContext context) => new ContactsDemo(),
     ),
     new GalleryItem(
       title: 'Animation',
       subtitle: 'Section organizer',
-      category: 'Demos',
+      category: 'Vignettes',
       routeName: AnimationDemo.routeName,
       buildRoute: (BuildContext context) => const AnimationDemo(),
     ),
     new GalleryItem(
       title: 'Video',
       subtitle: 'Video playback',
-      category: 'Demos',
+      category: 'Vignettes',
       routeName: VideoDemo.routeName,
       buildRoute: (BuildContext context) => const VideoDemo(),
     ),
@@ -373,7 +373,7 @@ List<GalleryItem> _buildGalleryItems() {
       new GalleryItem(
         title: 'Pesto',
         subtitle: 'Simple recipe browser',
-        category: 'Demos',
+        category: 'Vignettes',
         routeName: PestoDemo.routeName,
         buildRoute: (BuildContext context) => const PestoDemo(),
       ),

examples/flutter_gallery/test/example_code_display_test.dart

@@ -20,7 +20,7 @@ void main() {
 
 
     // Scroll the Buttons demo into view so that a tap will succeed
-    final Offset allDemosOrigin = tester.getTopRight(find.text('Demos'));
+    final Offset allDemosOrigin = tester.getTopRight(find.text('Vignettes'));
     final Finder button = find.text('Buttons');
     while (button.evaluate().isEmpty) {
       await tester.dragFrom(allDemosOrigin, const Offset(0.0, -200.0));

examples/flutter_gallery/test/simple_smoke_test.dart

@@ -37,7 +37,7 @@ void main() {
     await tester.pump(const Duration(seconds: 1)); // end animation
 
     // Open Demos
-    await tester.tap(find.text('Demos'));
+    await tester.tap(find.text('Vignettes'));
     await tester.pump(); // start animation
     await tester.pump(const Duration(seconds: 1)); // end animation
 

examples/flutter_gallery/test_driver/scroll_perf_test.dart

@@ -26,7 +26,7 @@ void main() {
         final SerializableFinder stockList = find.byValueKey('Gallery List');
         expect(stockList, isNotNull);
 
-        await driver.tap(find.text('Demos'));
+        await driver.tap(find.text('Vignettes'));
         await driver.tap(find.text('Components'));
         await driver.tap(find.text('Style'));