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

src/scanner.h

Index: src/scanner.h
diff --git a/src/scanner.h b/src/scanner.h
index 6d0d4dc8eddb52022f67cb1cdb01273695666373..ea4f74c1f71a5aa758c8871b05fe5c520b6bf446 100644
--- a/src/scanner.h
+++ b/src/scanner.h
@@ -373,13 +373,10 @@ class Scanner {
   Location peek_location() const { return next_.location; }
 
   bool literal_contains_escapes() const {
-    Location location = current_.location;
-    int source_length = (location.end_pos - location.beg_pos);
-    if (current_.token == Token::STRING) {
-      // Subtract delimiters.
-      source_length -= 2;
-    }
-    return current_.literal_chars->length() != source_length;
+    return LiteralContainsEscapes(current_);
+  }
+  bool next_literal_contains_escapes() const {
+    return LiteralContainsEscapes(next_);
   }
   bool is_literal_contextual_keyword(Vector<const char> keyword) {
     DCHECK_NOT_NULL(current_.literal_chars);
@@ -394,6 +391,8 @@ class Scanner {
   const AstRawString* NextSymbol(AstValueFactory* ast_value_factory);
   const AstRawString* CurrentRawSymbol(AstValueFactory* ast_value_factory);
 
+  bool IsNextEscapedReservedWord(LanguageMode language_mode, bool is_generator);
+
   double DoubleValue();
   bool ContainsDot();
   bool LiteralMatches(const char* data, int length, bool allow_escapes = true) {
@@ -689,6 +688,16 @@ class Scanner {
     return static_cast<int>(source_->pos()) - kCharacterLookaheadBufferSize;
   }
 
+  static bool LiteralContainsEscapes(const TokenDesc& token) {
+    Location location = token.location;
+    int source_length = (location.end_pos - location.beg_pos);
+    if (token.token == Token::STRING) {
+      // Subtract delimiters.
+      source_length -= 2;
+    }
+    return token.literal_chars->length() != source_length;
+  }
+
   UnicodeCache* unicode_cache_;
 
   // Buffers collecting literal strings, numbers, etc.