Change LicensePage's loading color from scaffoldBackgroundColor to cardColor (#64639)

* wrap LicensePage's loading widget with cardColor

* Set AnimatedSwitcer's duration in LicensePage to zero

* Remove AnimatedSwitcher

* Add test code for checking color is same

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

@@ -611,41 +611,40 @@ class _PackagesViewState extends State<_PackagesView> {
     return FutureBuilder<_LicenseData>(
       future: licenses,
       builder: (BuildContext context, AsyncSnapshot<_LicenseData> snapshot) {
-        return AnimatedSwitcher(
-          transitionBuilder: (Widget child, Animation<double> animation) => FadeTransition(opacity: animation, child: child),
-          duration: kThemeAnimationDuration,
-          child: LayoutBuilder(
-            key: ValueKey<ConnectionState>(snapshot.connectionState),
-            builder: (BuildContext context, BoxConstraints constraints) {
-              switch (snapshot.connectionState) {
-                case ConnectionState.done:
-                  _initDefaultDetailPage(snapshot.data, context);
-                  return ValueListenableBuilder<int>(
-                    valueListenable: widget.selectedId,
-                    builder: (BuildContext context, int selectedId, Widget _) {
-                      return Center(
-                        child: Material(
-                          color: Theme.of(context).cardColor,
-                          elevation: 4.0,
-                          child: Container(
-                            constraints: BoxConstraints.loose(const Size.fromWidth(600.0)),
-                            child: _packagesList(context, selectedId, snapshot.data, widget.isLateral),
-                          ),
+        return LayoutBuilder(
+          key: ValueKey<ConnectionState>(snapshot.connectionState),
+          builder: (BuildContext context, BoxConstraints constraints) {
+            switch (snapshot.connectionState) {
+              case ConnectionState.done:
+                _initDefaultDetailPage(snapshot.data, context);
+                return ValueListenableBuilder<int>(
+                  valueListenable: widget.selectedId,
+                  builder: (BuildContext context, int selectedId, Widget _) {
+                    return Center(
+                      child: Material(
+                        color: Theme.of(context).cardColor,
+                        elevation: 4.0,
+                        child: Container(
+                          constraints: BoxConstraints.loose(const Size.fromWidth(600.0)),
+                          child: _packagesList(context, selectedId, snapshot.data, widget.isLateral),
                         ),
-                      );
-                    },
-                  );
-                default:
-                  return Column(
+                      ),
+                    );
+                  },
+                );
+              default:
+                return Material(
+                    color: Theme.of(context).cardColor,
+                    child: Column(
                     mainAxisAlignment: MainAxisAlignment.start,
                     children: <Widget>[
                       widget.about,
                       const Center(child: CircularProgressIndicator()),
                     ],
-                  );
-              }
-            },
-          ),
+                  ),
+                );
+            }
+          },
         );
       },
     );

packages/flutter/test/material/about_test.dart

@@ -664,6 +664,53 @@ void main() {
 
     expect(box.localToGlobal(Offset.zero), equals(originalOffset.translate(0.0, -20.0)));
   });
+
+  testWidgets("LicensePage's color must be same whether loading or done", (WidgetTester tester) async {
+    const Color scaffoldColor = Color(0xFF123456);
+    const Color cardColor = Color(0xFF654321);
+
+    await tester.pumpWidget(MaterialApp(
+      theme: ThemeData.light().copyWith(
+        scaffoldBackgroundColor: scaffoldColor,
+        cardColor: cardColor,
+      ),
+      home: Scaffold(
+        body: Center(
+          child: Builder(
+            builder: (BuildContext context) => GestureDetector(
+              child: const Text('Show licenses'),
+              onTap: () {
+                showLicensePage(
+                  context: context,
+                  applicationName: 'MyApp',
+                  applicationVersion: '1.0.0',
+                );
+              }
+            ),
+          ),
+        ),
+      ),
+    ));
+
+    await tester.tap(find.text('Show licenses'));
+    await tester.pump();
+    await tester.pump();
+
+    // Check color when loading.
+    final List<Material> materialLoadings = tester.widgetList<Material>(find.byType(Material)).toList();
+    expect(materialLoadings.length, equals(4));
+    expect(materialLoadings[1].color, scaffoldColor);
+    expect(materialLoadings[2].color, cardColor);
+
+    await tester.pumpAndSettle();
+
+    // Check color when done.
+    expect(find.byKey(const ValueKey<ConnectionState>(ConnectionState.done)), findsOneWidget);
+    final List<Material> materialDones = tester.widgetList<Material>(find.byType(Material)).toList();
+    expect(materialDones.length, equals(3));
+    expect(materialDones[0].color, scaffoldColor);
+    expect(materialDones[1].color, cardColor);
+  });
 }
 
 class FakeLicenseEntry extends LicenseEntry {