Fix computation of documentationComment for class type aliases.

pkg/analyzer/test/generated/non_error_resolver_test.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.test.generated.non_error_resolver_test;
 
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/error.dart';
@@ skipping 17 matching lines @@
     Source source = addSource(r'''
 enum E { ONE }
 E e() {
   return E.TWO;
 }''');
     computeLibrarySourceErrors(source);
     assertNoErrors(source);
     verify([source]);
   }
 
+  void test_class_type_alias_documentationComment() {
+    Source source = addSource('''
+/**
+ * Documentation
+ */
+class C = D with E;
+
+class D {}
+class E {}''');
+    computeLibrarySourceErrors(source);
+    computeLibrarySourceErrors(source);
+    assertNoErrors(source);
+    verify([source]);
+    CompilationUnit unit = _getResolvedLibraryUnit(source);
+    ClassElement classC = unit.element.getType('C');
+    expect(classC.documentationComment, isNotNull);
+  }
+
   void test_ambiguousExport() {
     Source source = addSource(r'''
 library L;
 export 'lib1.dart';
 export 'lib2.dart';''');
     addNamedSource(
         "/lib1.dart",
         r'''
 library lib1;
 class M {}''');
@@ skipping 5994 matching lines @@
     reset();
   }
 
   void _check_wrongNumberOfParametersForOperator1(String name) {
     _check_wrongNumberOfParametersForOperator(name, "a");
   }
 
   CompilationUnit _getResolvedLibraryUnit(Source source) =>
       analysisContext.getResolvedCompilationUnit2(source, source);
 }