Speculative Revert "[parser] Removed unnecessary copies"

This reverts commit d16bce9d.

Reason for revert: Investigating what caused the redness here:
https://ci.chromium.org/p/v8/builders/luci.v8.ci/V8-Blink%20Mac/15097

Original change's description:
> [parser] Removed unnecessary copies
> 
> Bug: v8:8015
> Change-Id: I2ee074559484b9865dc1a27e6ea697ca311ee7ee
> Reviewed-on: https://chromium-review.googlesource.com/1185198
> Reviewed-by: Marja Hölttä <marja@chromium.org>
> Commit-Queue: Florian Sattler <sattlerf@google.com>
> Cr-Commit-Position: refs/heads/master@{#55327}

TBR=marja@chromium.org,sattlerf@google.com

Change-Id: I0344b11c2538a2755315dae7dd1f1ab62b8e069c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:8015
Reviewed-on: https://chromium-review.googlesource.com/1186441Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55343}

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 (const auto& declaration : parsing_result->declarations) {
+  for (auto declaration : parsing_result->declarations) {
     DeclareAndInitializeVariables(result, &(parsing_result->descriptor),
                                   &declaration, names, CHECK_OK);
   }