Serialize prefixes directly, without intermediate map.

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/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/type.dart' show DartType;
@@ skipping 248 matching lines @@
    */
   final List<UnlinkedImportBuilder> unlinkedImports = <UnlinkedImportBuilder>[];
 
   /**
    * The unlinked portion of the "references table".  This is the list of
    * objects which should be written to [UnlinkedUnit.references].
    */
   final List<UnlinkedReferenceBuilder> unlinkedReferences =
       <UnlinkedReferenceBuilder>[new UnlinkedReferenceBuilder()];
 
-  /**
-   * Map associating names used as prefixes in this compilation unit with their
-   * associated indices into [UnlinkedUnit.references].
-   */
-  final Map<String, int> prefixIndices = <String, int>{};
 
   /**
    * List of [_Scope]s currently in effect.  This is used to resolve type names
    * to type parameters within classes, typedefs, and executables, as well as
    * references to class members.
    */
   final List<_Scope> scopes = <_Scope>[];
 
   /**
    * True if 'dart:core' has been explicitly imported.
@@ skipping 622 matching lines @@
               b.reference = serializeReference(null, 'dynamic');
               return b;
             }
           }
           if (scope is _TypeParameterScope) {
             indexOffset += scope.length;
           }
         }
         b.reference = serializeReference(null, name);
       } else if (identifier is PrefixedIdentifier) {
-        int prefixIndex = prefixIndices.putIfAbsent(identifier.prefix.name,
-            () => serializeSimpleReference(identifier.prefix.name));
+        int prefixIndex = serializeSimpleReference(identifier.prefix.name);
         b.reference =
             serializeReference(prefixIndex, identifier.identifier.name);
       } else {
         throw new StateError(
             'Unexpected identifier type: ${identifier.runtimeType}');
       }
       if (typeArguments != null) {
         b.typeArguments =
             typeArguments.arguments.map(serializeTypeName).toList();
       }
@@ skipping 492 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;
 }