Add ImportElement and ExportElement

pkg/compiler/lib/src/elements/visitor.dart

Index: pkg/compiler/lib/src/elements/visitor.dart
diff --git a/pkg/compiler/lib/src/elements/visitor.dart b/pkg/compiler/lib/src/elements/visitor.dart
index 776922666a61e5688dbed9fa3aa0e0510a7e959c..23d526349b19e94a29d3ecb47500ef64ddf13cea 100644
--- a/pkg/compiler/lib/src/elements/visitor.dart
+++ b/pkg/compiler/lib/src/elements/visitor.dart
@@ -20,6 +20,8 @@ abstract class ElementVisitor<R, A> {
   R visitAmbiguousElement(AmbiguousElement e, A arg) => null;
   R visitCompilationUnitElement(CompilationUnitElement e, A arg) => null;
   R visitLibraryElement(LibraryElement e, A arg) => null;
+  R visitImportElement(ImportElement e, A arg) => null;
+  R visitExportElement(ExportElement e, A arg) => null;
   R visitPrefixElement(PrefixElement e, A arg) => null;
   R visitTypedefElement(TypedefElement e, A arg) => null;
   R visitVariableElement(VariableElement e, A arg) => null;
@@ -76,6 +78,16 @@ abstract class BaseElementVisitor<R, A> extends ElementVisitor<R, A> {
   }
 
   @override
+  R visitImportElement(ImportElement e, A arg) {
+    return visitElement(e, arg);
+  }
+
+  @override
+  R visitExportElement(ExportElement e, A arg) {
+    return visitElement(e, arg);
+  }
+
+  @override
   R visitPrefixElement(PrefixElement e, A arg) {
     return visitElement(e, arg);
   }