fasta scanner recovery and error code translation improvements

pkg/front_end/lib/src/fasta/scanner/token.dart

Index: pkg/front_end/lib/src/fasta/scanner/token.dart
diff --git a/pkg/front_end/lib/src/fasta/scanner/token.dart b/pkg/front_end/lib/src/fasta/scanner/token.dart
index 35067a2e04cce24eb47ab156400ef5d2820181a5..a380e48250348246fc5fa8e3e4407f0e68a7baf0 100644
--- a/pkg/front_end/lib/src/fasta/scanner/token.dart
+++ b/pkg/front_end/lib/src/fasta/scanner/token.dart
@@ -16,8 +16,6 @@ import 'precedence.dart'
         IDENTIFIER_INFO,
         IS_INFO,
         KEYWORD_INFO,
-        MULTI_LINE_COMMENT_INFO,
-        SINGLE_LINE_COMMENT_INFO,
         PrecedenceInfo;
 
 import 'token_constants.dart' show IDENTIFIER_TOKEN;
@@ -258,13 +256,21 @@ class SymbolToken extends Token {
 
   SymbolToken(this.info, int charOffset) : super(charOffset);
 
+  SymbolToken.eof(int charOffset)
+      : info = EOF_INFO,
+        super(charOffset) {
+    // EOF points to itself so there's always infinite look-ahead.
+    previousToken = this;
+    next = this;
+  }
+
   String get lexeme => info.value;
 
   String get stringValue => info.value;
 
   bool isIdentifier() => false;
 
-  String toString() => "SymbolToken($lexeme)";
+  String toString() => "SymbolToken(${info == EOF_INFO ? '-eof-' : lexeme})";
 
   bool get isEof => info == EOF_INFO;