enable lint prefer_for_elements_to_map_fromIterable (flutter#47726)

analysis_options.yaml

@@ -143,7 +143,7 @@ linter:
     - prefer_final_fields
     - prefer_final_in_for_each
     - prefer_final_locals
-    # - prefer_for_elements_to_map_fromIterable # not yet tested
+    - prefer_for_elements_to_map_fromIterable
     - prefer_foreach
     # - prefer_function_declarations_over_variables # not yet tested
     - prefer_generic_function_type_aliases

examples/flutter_gallery/lib/gallery/app.dart

@@ -51,11 +51,9 @@ class _GalleryAppState extends State<GalleryApp> {
     // For a different example of how to set up an application routing table
     // using named routes, consider the example in the Navigator class documentation:
     // https://docs.flutter.io/flutter/widgets/Navigator-class.html
-    return Map<String, WidgetBuilder>.fromIterable(
-      kAllGalleryDemos,
-      key: (dynamic demo) => '${(demo as GalleryDemo).routeName}',
-      value: (dynamic demo) => (demo as GalleryDemo).buildRoute,
-    );
+    return <String, WidgetBuilder>{
+      for (final GalleryDemo demo in kAllGalleryDemos) demo.routeName: demo.buildRoute,
+    };
   }
 
   @override

examples/flutter_gallery/lib/gallery/demos.dart

@@ -579,9 +579,7 @@ final Map<GalleryDemoCategory, List<GalleryDemo>> kGalleryCategoryToDemos =
     },
   );
 
-final Map<String, String> kDemoDocumentationUrl =
-    Map<String, String>.fromIterable(
-      kAllGalleryDemos.where((GalleryDemo demo) => demo.documentationUrl != null),
-      key: (dynamic demo) => (demo as GalleryDemo).routeName,
-      value: (dynamic demo) => (demo as GalleryDemo).documentationUrl,
-    );
+final Map<String, String> kDemoDocumentationUrl = <String, String>{
+  for (final GalleryDemo demo in kAllGalleryDemos)
+    if (demo.documentationUrl != null) demo.routeName: demo.documentationUrl,
+};