Add debugging support for issue 25302

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 2485 matching lines @@
     }
     if (element == null) {
       if (_enclosingClass != null) {
         element =
             _findIdentifier(_enclosingClass.typeParameters, parameterName);
       } else if (_enclosingAlias != null) {
         element =
             _findIdentifier(_enclosingAlias.typeParameters, parameterName);
       }
     }
+    if (element == null) {
+      String name = parameterName.name;
+      int offset = parameterName.offset;
+      _mismatch(
+          'Could not find type parameter with name "$name" at $offset', node);
+    }
     super.visitTypeParameter(node);
     _resolveMetadata(node.metadata, element);
     return null;
   }
 
   @override
   Object visitVariableDeclaration(VariableDeclaration node) {
     VariableElement element = null;
     SimpleIdentifier variableName = node.name;
     if (_enclosingExecutable != null) {
@@ skipping 10269 matching lines @@
     nonFields.add(node);
     return null;
   }
 
   @override
   Object visitNode(AstNode node) => node.accept(TypeResolverVisitor_this);
 
   @override
   Object visitWithClause(WithClause node) => null;
 }