Make sure that a WidgetsApp doesn't crash in 0x0 environment (#180224)

This is my attempt to handle
https://github.com/flutter/flutter/issues/6537 for the WidgetsApp
widget.

Co-authored-by: Tong Mu <dkwingsmt@users.noreply.github.com>

packages/flutter/test/widgets/app_test.dart

diff --git a/packages/flutter/test/widgets/app_test.dart b/packages/flutter/test/widgets/app_test.dart
index 48bf5d7..b458d9e 100644
--- a/packages/flutter/test/widgets/app_test.dart
+++ b/packages/flutter/test/widgets/app_test.dart
@@ -778,6 +778,17 @@
       variant: const TargetPlatformVariant(<TargetPlatform>{TargetPlatform.android}),
     );
   });
+
+  testWidgets('WidgetsApp does not crash at zero area', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      Center(
+        child: SizedBox.shrink(
+          child: WidgetsApp(builder: (_, _) => const Text('X'), color: const Color(0xFFAABBCC)),
+        ),
+      ),
+    );
+    expect(tester.getSize(find.byType(WidgetsApp)), Size.zero);
+  });
 }
 
 typedef SimpleRouterDelegateBuilder =