Various scanner fixes:

dart/frog/leg/scanner/token.dart

 // Copyright (c) 2011, 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.
 
 final int EOF_TOKEN = 0;
 
 final int KEYWORD_TOKEN = $k;
 final int IDENTIFIER_TOKEN = $a;
 final int DOUBLE_TOKEN = $d;
 final int INT_TOKEN = $i;
 final int HEXADECIMAL_TOKEN = $x;
 final int STRING_TOKEN = $SQ;
+final int STRING_INTERPOLATION_TOKEN = $SQ + 128;
 
 final int AMPERSAND_TOKEN = $AMPERSAND;
 final int BACKPING_TOKEN = $BACKPING;
 final int BACKSLASH_TOKEN = $BACKSLASH;
 final int BANG_TOKEN = $BANG;
 final int BAR_TOKEN = $BAR;
 final int COLON_TOKEN = $COLON;
 final int COMMA_TOKEN = $COMMA;
 final int EQ_TOKEN = $EQ;
 final int GT_TOKEN = $GT;
@@ skipping 88 matching lines @@
   }
 
   String toString() => stringValue;
 }
 
 class BeginGroupToken extends StringToken {
   Token endGroup;
   BeginGroupToken(int kind, String value, int charOffset)
     : super(kind, value, charOffset);
 }