Do not penalize performance when --harmony-species is off

This patch ensures that the species protector does not cause
any slow paths to be taken when --harmony-species is off by
refraining from writing to and reading from the protector
when the flag is off.

BUG=chromium:606207
R=adamk
LOG=Y

Review URL: https://codereview.chromium.org/1918383002

Cr-Commit-Position: refs/heads/master@{#35800}

src/isolate.cc

@@ -2554,6 +2554,7 @@ bool Isolate::IsFastArrayConstructorPrototypeChainIntact() {
 }
 
 bool Isolate::IsArraySpeciesLookupChainIntact() {
+  if (!FLAG_harmony_species) return true;
   // Note: It would be nice to have debug checks to make sure that the
   // species protector is accurate, but this would be hard to do for most of
   // what the protector stands for:
@@ -2572,6 +2573,7 @@ bool Isolate::IsArraySpeciesLookupChainIntact() {
 }
 
 void Isolate::InvalidateArraySpeciesProtector() {
+  if (!FLAG_harmony_species) return;
   DCHECK(factory()->species_protector()->value()->IsSmi());
   DCHECK(IsArraySpeciesLookupChainIntact());
   PropertyCell::SetValueWithInvalidation(