Fix computation of documentationComment for class type aliases.

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/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
@@ skipping 2737 matching lines @@
     SimpleIdentifier className = node.name;
     ClassElementImpl element = new ClassElementImpl.forNode(className);
     element.abstract = node.abstractKeyword != null;
     element.mixinApplication = true;
     List<TypeParameterElement> typeParameters = holder.typeParameters;
     element.typeParameters = typeParameters;
     List<DartType> typeArguments = _createTypeParameterTypes(typeParameters);
     InterfaceTypeImpl interfaceType = new InterfaceTypeImpl(element);
     interfaceType.typeArguments = typeArguments;
     element.type = interfaceType;
+    _setDoc(element, node);
     _currentHolder.addType(element);
     className.staticElement = element;
     holder.validate();
     return null;
   }
 
   @override
   Object visitConstructorDeclaration(ConstructorDeclaration node) {
     _isValidMixin = false;
     ElementHolder holder = new ElementHolder();
@@ skipping 10760 matching lines @@
     nonFields.add(node);
     return null;
   }
 
   @override
   Object visitNode(AstNode node) => node.accept(TypeResolverVisitor_this);
 
   @override
   Object visitWithClause(WithClause node) => null;
 }