Use summary IDL file for interface classes.

pkg/analyzer/lib/src/summary/summarize_ast.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.
 
 library serialization.summarize_ast;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/src/generated/scanner.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
 import 'package:analyzer/src/summary/format.dart';
+import 'package:analyzer/src/summary/idl.dart';
 import 'package:analyzer/src/summary/public_namespace_computer.dart';
 import 'package:analyzer/src/summary/summarize_const_expr.dart';
 
 /**
  * Serialize all the declarations in [compilationUnit] to an unlinked summary.
  */
 UnlinkedUnitBuilder serializeAstUnlinked(CompilationUnit compilationUnit) {
   return new _SummarizeAstVisitor().serializeCompilationUnit(compilationUnit);
 }
 
@@ skipping 854 matching lines @@
 /**
  * A [_TypeParameterScope] is a [_Scope] which defines [_ScopedTypeParameter]s.
  */
 class _TypeParameterScope extends _Scope {
   /**
    * Get the number of [_ScopedTypeParameter]s defined in this
    * [_TypeParameterScope].
    */
   int get length => _definedNames.length;
 }