[scanner] Keep literals around for FUTURE_STRICT_RESERVED_KEYWORD.

BUG=chromium:690003

Change-Id: I0f80911426e9b201be61af313b4b5cacbb357bb5
Reviewed-on: https://chromium-review.googlesource.com/443329Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Daniel Vogelheim <vogelheim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43236}

src/parsing/scanner.cc

@@ -1489,7 +1489,9 @@ Token::Value Scanner::ScanIdentifierOrKeyword() {
     Vector<const uint8_t> chars = next_.literal_chars->one_byte_literal();
     Token::Value token =
         KeywordOrIdentifierToken(chars.start(), chars.length());
-    if (token == Token::IDENTIFIER) literal.Complete();
+    if (token == Token::IDENTIFIER ||
+        token == Token::FUTURE_STRICT_RESERVED_WORD)
+      literal.Complete();
     return token;
   }
   literal.Complete();