Fix computation of documentationComment for class type aliases.

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

Index: pkg/analyzer/lib/src/generated/resolver.dart
diff --git a/pkg/analyzer/lib/src/generated/resolver.dart b/pkg/analyzer/lib/src/generated/resolver.dart
index 113f4d77ee1473ecc1e8fd461b1c49b29c4a0969..0ef7e892bc21f26d855e6cc7e800aea7fd943081 100644
--- a/pkg/analyzer/lib/src/generated/resolver.dart
+++ b/pkg/analyzer/lib/src/generated/resolver.dart
@@ -2755,6 +2755,7 @@ class ElementBuilder extends RecursiveAstVisitor<Object> {
     InterfaceTypeImpl interfaceType = new InterfaceTypeImpl(element);
     interfaceType.typeArguments = typeArguments;
     element.type = interfaceType;
+    _setDoc(element, node);
     _currentHolder.addType(element);
     className.staticElement = element;
     holder.validate();