[parser] Removed unnecessary copies

Bug: v8:8015
Change-Id: I2ee074559484b9865dc1a27e6ea697ca311ee7ee
Reviewed-on: https://chromium-review.googlesource.com/1185198Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Florian Sattler <sattlerf@google.com>
Cr-Commit-Position: refs/heads/master@{#55327}

src/parsing/parser.cc

@@ -1404,7 +1404,7 @@ Block* Parser::BuildInitializationBlock(
     DeclarationParsingResult* parsing_result,
     ZonePtrList<const AstRawString>* names, bool* ok) {
   Block* result = factory()->NewBlock(1, true);
-  for (auto declaration : parsing_result->declarations) {
+  for (const auto& declaration : parsing_result->declarations) {
     DeclareAndInitializeVariables(result, &(parsing_result->descriptor),
                                   &declaration, names, CHECK_OK);
   }