Introduce code to generate UnlinkedPublicNamespace directly from an AST.

pkg/analyzer/tool/summary/idl.dart

 // Copyright (c) 2015, 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.
 
 /**
  * This file is an "idl" style description of the summary format.  It is not
  * executed directly; instead it is parsed and transformed into code that
  * implements the summary format.
  *
  * The code generation process introduces the following non-typical semantics:
@@ skipping 554 matching lines @@
    * The kind of object referred to by the name.
    */
   PrelinkedReferenceKind kind;
 }
 
 /**
  * Unlinked summary information about what a compilation unit contributes to a
  * library's public namespace.  This is the subset of [UnlinkedUnit] that is
  * required from dependent libraries in order to perform prelinking.
  */
+@topLevel
 class UnlinkedPublicNamespace {
   /**
    * Public names defined in the compilation unit.
    *
    * TODO(paulberry): consider sorting these names to reduce unnecessary
    * relinking.
    */
   List<UnlinkedPublicName> names;
 
   /**
@@ skipping 197 matching lines @@
   /**
    * Indicates whether the variable is declared using the `const` keyword.
    */
   bool isConst;
 
   /**
    * Indicates whether this variable lacks an explicit type declaration.
    */
   bool hasImplicitType;
 }