fix #27259, implement covariance checking for strong mode and DDC

pkg/analyzer/lib/src/generated/resolver.dart

Index: pkg/analyzer/lib/src/generated/resolver.dart
diff --git a/pkg/analyzer/lib/src/generated/resolver.dart b/pkg/analyzer/lib/src/generated/resolver.dart
index e2c839602f37b32f032c86fe00755fe53031bf37..3500d4a3d96cfc77daf03d3ed9eab30674f53663 100644
--- a/pkg/analyzer/lib/src/generated/resolver.dart
+++ b/pkg/analyzer/lib/src/generated/resolver.dart
@@ -6515,10 +6515,10 @@ class ResolverVisitor extends ScopedVisitor {
         !FunctionTypeImpl.relate(
             expectedClosureType,
             staticClosureType,
-            (DartType t, DartType s, _, __) =>
-                (t as TypeImpl).isMoreSpecificThan(s),
+            (s, t) => true,
             new TypeSystemImpl(typeProvider).instantiateToBounds,
-            returnRelation: (s, t) => true)) {
+            parameterRelation: (t, s) =>
+                (t.type as TypeImpl).isMoreSpecificThan(s.type))) {
       return;
     }
     // set propagated type for the closure