improve static type analysis for `await for`

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

Index: pkg/analyzer/lib/src/generated/error_verifier.dart
diff --git a/pkg/analyzer/lib/src/generated/error_verifier.dart b/pkg/analyzer/lib/src/generated/error_verifier.dart
index ec9559a0fee3b5cf31e84c344daf6d4ebb463e76..e1c8e11fb4ee511b3dae29e07ea27f9ddaaf1461 100644
--- a/pkg/analyzer/lib/src/generated/error_verifier.dart
+++ b/pkg/analyzer/lib/src/generated/error_verifier.dart
@@ -1312,13 +1312,8 @@ class ErrorVerifier extends RecursiveAstVisitor<Object> {
       isGetter = accessorElement.isGetter;
       isSetter = accessorElement.isSetter;
     }
-    String executableElementName = executableElement.name;
     FunctionType overridingFT = executableElement.type;
     FunctionType overriddenFT = overriddenExecutable.type;
-    InterfaceType enclosingType = _enclosingClass.type;
-    overriddenFT = _inheritanceManager
-        .substituteTypeArgumentsInMemberFromInheritance(
-            overriddenFT, executableElementName, enclosingType);
     if (overridingFT == null || overriddenFT == null) {
       return false;
     }
@@ -4483,15 +4478,7 @@ class ErrorVerifier extends RecursiveAstVisitor<Object> {
         // method, so skip it.
         if ((elt is MethodElement && !elt.isAbstract) ||
             (elt is PropertyAccessorElement && !elt.isAbstract)) {
-          // Since we are comparing two function types, we need to do the
-          // appropriate type substitutions first ().
-          FunctionType foundConcreteFT = _inheritanceManager
-              .substituteTypeArgumentsInMemberFromInheritance(
-                  concreteType, memberName, enclosingType);
-          FunctionType requiredMemberFT = _inheritanceManager
-              .substituteTypeArgumentsInMemberFromInheritance(
-                  requiredMemberType, memberName, enclosingType);
-          if (_typeSystem.isSubtypeOf(foundConcreteFT, requiredMemberFT)) {
+          if (_typeSystem.isSubtypeOf(concreteType, requiredMemberType)) {
             continue;
           }
         }