Fixes issues in string interpolation tests

frog/tokenizer.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.
 // Generated by scripts/tokenizer_gen.py.
 
 class InterpStack {
   InterpStack next, previous;
   final int quote;
   final bool isMultiline;
   int depth;
@@ skipping 361 matching lines @@
 
   Token finishDot() {
     if (isDigit(_peekChar())) {
       eatDigits();
       return finishNumberExtra(TokenKind.DOUBLE);
     } else {
       return _finishToken(TokenKind.DOT);
     }
   }
 
-  Token finishIdentifier() {
-    while (_index < _text.length) {
-      if (!isIdentifierPart(_text.charCodeAt(_index++))) {
-        _index--;
-        break;
+  Token finishIdentifier(int ch) {
+    if (_interpStack != null && _interpStack.depth == -1) {
+      _interpStack.depth = 0;
+      if (ch == 36/*$*/) {
+        // illegal character after $ in string interpolation
+        return _errorToken();
+      }
+      while (_index < _text.length) {
+        if (!isInterpIdentifierPart(_text.charCodeAt(_index++))) {
+          _index--;
+          break;
+        }
+      }
+    } else {
+      while (_index < _text.length) {
+        if (!isIdentifierPart(_text.charCodeAt(_index++))) {
+          _index--;
+          break;
+        }
       }
     }
     int kind = getIdentifierKind();
-    if (_interpStack != null && _interpStack.depth == -1) {
-      _interpStack.depth = 0;
-    }
     if (kind == TokenKind.IDENTIFIER) {
       return _finishToken(TokenKind.IDENTIFIER);
     } else {
       return _finishToken(kind);
     }
   }
 }