fasta scanner recovery and error code translation improvements

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

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style licenset hat can be found in the LICENSE file.
 
 library fasta.scanner.recover;
 
-import 'token.dart' show StringToken, Token;
+import 'token.dart' show StringToken, SymbolToken, Token;
 
 import 'error_token.dart' show NonAsciiIdentifierToken, ErrorKind, ErrorToken;
 
 import 'precedence.dart' as Precedence;
 
 import 'precedence.dart' show PrecedenceInfo;
 
 /// Recover from errors in [tokens]. The original sources are provided as
 /// [bytes]. [lineStarts] are the beginning character offsets of lines, and
 /// must be updated if recovery is performed rewriting the original source
@@ skipping 130 matching lines @@
     if (current is ErrorToken) {
       ErrorToken first = current;
       Token next = current;
       bool treatAsWhitespace = false;
       do {
         current = next;
         if (errorTail == null) {
           error = next;
         } else {
           errorTail.next = next;
+          next.previousToken = errorTail;
         }
         errorTail = next;
         next = next.next;
       } while (next is ErrorToken && first.errorCode == next.errorCode);
 
       switch (first.errorCode) {
         case ErrorKind.Encoding:
         case ErrorKind.NonAsciiWhitespace:
         case ErrorKind.AsciiControlCharacter:
           treatAsWhitespace = true;
@@ skipping 38 matching lines @@
         default:
           treatAsWhitespace = true;
           break;
       }
       if (treatAsWhitespace) continue;
     }
     if (goodTail == null) {
       good = current;
     } else {
       goodTail.next = current;
+      current.previousToken = goodTail;
     }
     beforeGoodTail = goodTail;
     goodTail = current;
   }
 
-  errorTail.next = good;
+  error.previousToken = new SymbolToken.eof(-1)..next = error;
+  Token tail;
+  if (good != null) {
+    errorTail.next = good;
+    good.previousToken = errorTail;
+    tail = goodTail;
+  } else {
+    tail = errorTail;
+  }
+  if (!tail.isEof)
+    tail.next = new SymbolToken.eof(tail.end)..previousToken = tail;
   return error;
 }
 
 Token synthesizeToken(int charOffset, String value, PrecedenceInfo info) {
   return new StringToken.fromString(info, value, charOffset);
 }
 
 Token skipToEof(Token token) {
   while (!token.isEof) {
     token = token.next;
   }
   return token;
 }
 
 String closeBraceFor(String openBrace) {
   return const {
     '(': ')',
     '[': ']',
     '{': '}',
     '<': '>',
     r'${': '}',
   }[openBrace];
 }