[parser] Set intial size for reported_errors_ vector

Changing reported_errors_ from a ZoneList to a ZoneVector caused
regressions in Octane/CodeLoad and some other parsing benchmarks. This
could be because we don't give the vector an initial size.

Change-Id: I42c6ae063681dc3490dbab260085e801e24ac569
Reviewed-on: https://chromium-review.googlesource.com/1186328Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55335}

src/parsing/parser-base.h

@@ -1592,7 +1592,7 @@ ParserBase<Impl>::FunctionState::FunctionState(
       outer_function_state_(*function_state_stack),
       scope_(scope),
       destructuring_assignments_to_rewrite_(scope->zone()),
-      reported_errors_(scope_->zone()),
+      reported_errors_(16, scope_->zone()),
       dont_optimize_reason_(BailoutReason::kNoReason),
       suspend_count_(0),
       next_function_is_likely_called_(false),