Use summary IDL file for interface classes.

pkg/analyzer/lib/src/summary/public_namespace_computer.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.
 
 library analyzer.src.summary.public_namespace_visitor;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/src/summary/format.dart';
+import 'package:analyzer/src/summary/idl.dart';
 
 /**
  * Compute the public namespace portion of the summary for the given [unit],
  * which is presumed to be an unresolved AST.
  */
 UnlinkedPublicNamespaceBuilder computePublicNamespace(CompilationUnit unit) {
   _PublicNamespaceVisitor visitor = new _PublicNamespaceVisitor();
   unit.accept(visitor);
   return new UnlinkedPublicNamespaceBuilder(
       names: visitor.names, exports: visitor.exports, parts: visitor.parts);
@@ skipping 132 matching lines @@
 
   @override
   visitVariableDeclaration(VariableDeclaration node) {
     String name = node.name.name;
     addNameIfPublic(name, ReferenceKind.topLevelPropertyAccessor, 0);
     if (!node.isFinal && !node.isConst) {
       addNameIfPublic('$name=', ReferenceKind.topLevelPropertyAccessor, 0);
     }
   }
 }