Handle escapes in string literals.

frog/leg/scanner/scanner.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.
 
 interface Scanner {
   Token tokenize();
 }
 
 /**
  * Common base class for a Dart scanner.
@@ skipping 611 matching lines @@
         return next;
       }
     }
     if (raw) {
       return tokenizeSingleLineRawString(next, q, start);
     } else {
       return tokenizeSingleLineString(next, q, start);
     }
   }
 
+  static bool isHexDigit(int character) {
+    if ($0 <= character && character <= $9) return true;
+    character |= 0x20;
+    return ($a <= character && character <= $f);
+  }
+
   int tokenizeSingleLineString(int next, int q1, int start) {
     while (next !== $EOF) {
       if (next === q1) {
         appendByteStringToken(STRING_INFO, utf8String(start, 0));
         return advance();
       } else if (next === $BACKSLASH) {
         next = advance();
         if (next === $EOF) {
           throw new MalformedInputException(charOffset);
         }
@@ skipping 67 matching lines @@
     }
     return next;
   }
 }
 
 class MalformedInputException {
   final message;
   MalformedInputException(this.message);
   toString() => message.toString();
 }