[es6] early error when Identifier is an escaped reserved word

src/token.h

Index: src/token.h
diff --git a/src/token.h b/src/token.h
index 2443e842386a04b9c6a8f11d1b4f6336ab6314c7..fea15e32aeb2e618912a077d2b8b0e3abf080e82 100644
--- a/src/token.h
+++ b/src/token.h
@@ -163,6 +163,8 @@ namespace internal {
                                                                      \
   /* Illegal token - not able to scan. */                            \
   T(ILLEGAL, "ILLEGAL", 0)                                           \
+  T(ESCAPED_KEYWORD, NULL, 0)                                        \
+  T(ESCAPED_STRICT_RESERVED_WORD, NULL, 0)                           \
                                                                      \
   /* Scanner-internal use only. */                                   \
   T(WHITESPACE, NULL, 0)                                             \
@@ -200,6 +202,7 @@ class Token {
     switch (tok) {
       case IDENTIFIER:
         return true;
+      case ESCAPED_STRICT_RESERVED_WORD:
       case FUTURE_STRICT_RESERVED_WORD:
       case LET:
       case STATIC: