Introduce code to generate summaries from an element model.

pkg/analyzer/tool/summary/idl_model.dart

Index: pkg/analyzer/tool/summary/idl_model.dart
diff --git a/pkg/analyzer/tool/summary/idl_model.dart b/pkg/analyzer/tool/summary/idl_model.dart
index d0089eac4794a6eb2aa0d53e46b9d2d8dac83092..8cd22905b26c1544aef35ec4be97d8990a1fe789 100644
--- a/pkg/analyzer/tool/summary/idl_model.dart
+++ b/pkg/analyzer/tool/summary/idl_model.dart
@@ -17,6 +17,13 @@ class ClassDeclaration {
    * Fields defined in the class.
    */
   final Map<String, FieldType> fields = <String, FieldType>{};
+
+/**
+ * Indicates whether the class has the `topLevel` annotation.
+ */
+  final bool isTopLevel;
+
+  ClassDeclaration(this.isTopLevel);
 }
 
 /**