Add helper methods for skipping Dart VM native bodies.

pkg/front_end/lib/src/fasta/parser/error_kind.dart

Index: pkg/front_end/lib/src/fasta/parser/error_kind.dart
diff --git a/pkg/front_end/lib/src/fasta/parser/error_kind.dart b/pkg/front_end/lib/src/fasta/parser/error_kind.dart
index d832df12d45fc3288673aa278a41746ef65be31b..6ee9eb87650dfe1ec72943ffa9c45a5ab94009a3 100644
--- a/pkg/front_end/lib/src/fasta/parser/error_kind.dart
+++ b/pkg/front_end/lib/src/fasta/parser/error_kind.dart
@@ -4,6 +4,7 @@
 
 library fasta.parser.error_kind;
 
+/// Kinds of error codes.
 enum ErrorKind {
   AsciiControlCharacter,
   EmptyNamedParameterList,
@@ -13,7 +14,12 @@ enum ErrorKind {
   ExpectedBody,
   ExpectedButGot,
   ExpectedClassBody,
+
+  /// This error code can be used to support non-compliant (with respect to
+  /// Dart Language Specification) Dart VM native clauses. See
+  /// [dart_vm_native.dart].
   ExpectedClassBodyToSkip,
+
   ExpectedDeclaration,
   ExpectedExpression,
   ExpectedFunctionBody,