When a name is both exported and defined locally, the name is defined.

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/generated/utilities_dart.dart';
 import 'package:analyzer/src/summary/format.dart';
 import 'package:analyzer/src/summary/idl.dart';
 import 'package:analyzer/src/summary/name_filter.dart';
 
 /**
@@ skipping 266 matching lines @@
                   unitNum, dependency, name.numTypeParameters, namespace));
         } else {
           aggregated.add(
               name.name,
               new _Meaning(
                   unitNum, name.kind, dependency, name.numTypeParameters));
         }
       }
     }
 
+    aggregated.rememberLibraryNames();
+
     dependencyToPublicNamespace.add(aggregated);
     return aggregated;
   }
 
   /**
    * Compute the export namespace for the library whose URI is reachable from
    * [definingUnit] via [relativeUri], by aggregating together public namespace
    * information from the library and the transitive closure of its exports.
    *
    * If [relativeUri] is `null` (meaning the export namespace of [definingUnit]
@@ skipping 10 matching lines @@
             getImportCached(relativeUri);
         if (exportedNamespace != null) {
           for (UnlinkedExportPublic export in exportedNamespace.exports) {
             String relativeExportUri =
                 _selectUri(export.uri, export.configurations);
             String exportUri = resolveUri(relativeUri, relativeExportUri);
             NameFilter newFilter = filter.merge(
                 new NameFilter.forUnlinkedCombinators(export.combinators));
             aggregatePublicNamespace(exportUri)
                 .forEach((String name, _Meaning meaning) {
-              if (newFilter.accepts(name)) {
+              if (newFilter.accepts(name) &&
+                  !exportNamespace.definesLibraryName(name)) {
                 exportNamespace.add(name, meaning);
               }
             });
             chaseExports(newFilter, exportUri, seenUris);
           }
         }
         seenUris.remove(relativeUri);
       }
     }
 
@@ skipping 276 matching lines @@
   String _selectUri(
       String defaultUri, List<UnlinkedConfiguration> configurations) {
     for (UnlinkedConfiguration configuration in configurations) {
       if (getDeclaredVariable(configuration.name) == configuration.value) {
         return configuration.uri;
       }
     }
     return defaultUri;
   }
 }