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

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

Index: pkg/analyzer/lib/src/summary/prelink.dart
diff --git a/pkg/analyzer/lib/src/summary/prelink.dart b/pkg/analyzer/lib/src/summary/prelink.dart
index 31fa6a5fe098ee1cab431e4752e2bb8ad40d467b..6005808e3826592d8598d8f57b69d2939b0ba343 100644
--- a/pkg/analyzer/lib/src/summary/prelink.dart
+++ b/pkg/analyzer/lib/src/summary/prelink.dart
@@ -284,6 +284,8 @@ class _Prelinker {
       }
     }
 
+    aggregated.rememberLibraryNames();
+
     dependencyToPublicNamespace.add(aggregated);
     return aggregated;
   }
@@ -314,7 +316,8 @@ class _Prelinker {
                 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);
               }
             });