Fix more strong mode errors in analyzer

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

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.src.generated.resolver;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 7525 matching lines @@
       return null;
     }
 
     if (fnType.typeFormals.length != typeParameters.length) {
       // A subtype cannot have different number of type formals.
       return null;
     }
 
     // Same number of type formals. Instantiate the function type so its
     // parameter and return type are in terms of the surrounding context.
-    return fnType.instantiate(
-        typeParameters.map((t) => t.name.staticElement.type).toList());
+    return fnType.instantiate(typeParameters
+        .map((TypeParameter t) =>
+            (t.name.staticElement as TypeParameterElement).type)
+        .toList());
   }
 
   /**
    * If it is appropriate to do so, override the current type of the static and propagated elements
    * associated with the given expression with the given type. Generally speaking, it is appropriate
    * if the given type is more specific than the current type.
    *
    * @param expression the expression used to access the static and propagated elements whose types
    *          might be overridden
    * @param potentialType the potential type of the elements
@@ skipping 5415 matching lines @@
     nonFields.add(node);
     return null;
   }
 
   @override
   Object visitNode(AstNode node) => node.accept(TypeResolverVisitor_this);
 
   @override
   Object visitWithClause(WithClause node) => null;
 }