Fix bad reference in string interpolation.

dart/sdk/lib/_internal/compiler/implementation/scanner/scanner.dart

 // Copyright (c) 2012, 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 license that can be found in the LICENSE file.
 
 part of scanner;
 
 abstract class Scanner {
   Token tokenize();
 
   factory Scanner(SourceFile file, {bool includeComments: false}) {
@@ skipping 182 matching lines @@
 
   Token tokenize() {
     while (!atEndOfFile()) {
       int next = advance();
       while (!identical(next, $EOF)) {
         next = bigSwitch(next);
       }
       if (atEndOfFile()) {
         appendEofToken();
       } else {
-        error('Unexpected $EOF byte in input.');
+        error('Unexpected ${$EOF} byte in input.');
       }
     }
 
     if (file != null) {
       file.length = stringOffset;
       // One additional line start at the end, see [SourceFile.lineStarts].
       lineStarts.add(stringOffset + 1);
       file.lineStarts = lineStarts;
     }
 
@@ skipping 867 matching lines @@
     // ignore the [close] token (assuming it's correct), then the error will be
     // reported when parsing the [next] token.
 
     Token next = new StringToken.fromString(
         BAD_INPUT_INFO, error, begin.charOffset, canonicalize: true);
     begin.endGroup = close;
     close.next = next;
     next.next = begin.next;
   }
 }