Use summary IDL file for interface classes.

pkg/analyzer/lib/src/summary/prelink.dart

 // Copyright (c) 2016, 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.
 
 import 'package:analyzer/src/summary/format.dart';
+import 'package:analyzer/src/summary/idl.dart';
 import 'package:analyzer/src/summary/name_filter.dart';
 
 /**
  * Create a [LinkedLibraryBuilder] corresponding to the given
  * [definingUnit], which should be the defining compilation unit for a library.
  * Compilation units referenced by the defining compilation unit via `part`
  * declarations will be retrieved using [getPart].  Public namespaces for
  * libraries referenced by the defining compilation unit via `import`
  * declarations (and files reachable from them via `part` and `export`
  * declarations) will be retrieved using [getImport].
@@ skipping 483 matching lines @@
    * [sourceUri] is also relative.
    */
   String resolveUri(String sourceUri, String relativeUri) {
     if (sourceUri == null) {
       return relativeUri;
     } else {
       return Uri.parse(sourceUri).resolve(relativeUri).toString();
     }
   }
 }