[null-safety] fix Scene.toImage declaration (flutter#21983)

Jonah Williams · web-flow · commit 326157ee7eac · 2020-10-19T22:52:19.000-07:00
diff --git a/lib/ui/compositing.dart b/lib/ui/compositing.dart
@@ -37,7 +37,7 @@ class Scene extends NativeFieldWrapperClass2 {
     );
   }
 
-  String _toImage(int width, int height, _Callback<_Image> callback) native 'Scene_toImage';
+  String? _toImage(int width, int height, _Callback<_Image> callback) native 'Scene_toImage';
 
   /// Releases the resources used by this scene.
   ///

Original file line number	Diff line number	Diff line change
`@@ -37,7 +37,7 @@ class Scene extends NativeFieldWrapperClass2 {`
`37`	`37`	`);`
`38`	`38`	`}`
`39`	`39`
`40`		`- String _toImage(int width, int height, _Callback<_Image> callback) native 'Scene_toImage';`
	`40`	`+ String? _toImage(int width, int height, _Callback<_Image> callback) native 'Scene_toImage';`
`41`	`41`
`42`	`42`	`/// Releases the resources used by this scene.`
`43`	`43`	`///`