Remove DirectoryException and LinkException from dart:io and use FileException instaed.

sdk/lib/_internal/dartdoc/lib/src/export_map.dart

Index: sdk/lib/_internal/dartdoc/lib/src/export_map.dart
diff --git a/sdk/lib/_internal/dartdoc/lib/src/export_map.dart b/sdk/lib/_internal/dartdoc/lib/src/export_map.dart
index 169b0e99ef0863e0e9bceae93288e5f2eead756a..0dbe107c535ca8a90270fae5c8f95355ce058754 100644
--- a/sdk/lib/_internal/dartdoc/lib/src/export_map.dart
+++ b/sdk/lib/_internal/dartdoc/lib/src/export_map.dart
@@ -46,7 +46,7 @@ class ExportMap {
       var importsAndExports;
       try {
         importsAndExports = _importsAndExportsForFile(path, packageRoot);
-      } on FileException catch (_) {
+      } on FileSystemException catch (_) {
         // Ignore unreadable/nonexistent files.
         return;
       }