[api] Fill FastTemplateCache with holes

The FastTemplateCache gets filled with undefiend when created and then
with holes when it grows causing a mismatch.

This hasn't been a problem so far as the FastTemplateCache is always
initialized to the max size but it could cause problems in the future
if this is changed.

Bug: v8:11289
Change-Id: I8dabce101b25d9f0057183c88f507873d973f2a8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2608472Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Sathya Gunasekaran  <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71939}

src/api/api-natives.cc

@@ -293,7 +293,7 @@ MaybeHandle<JSObject> ProbeInstantiationsCache(
     FixedArray fast_cache =
         native_context->fast_template_instantiations_cache();
     Handle<Object> object{fast_cache.get(serial_number - 1), isolate};
-    if (object->IsUndefined(isolate)) return {};
+    if (object->IsTheHole(isolate)) return {};
     return Handle<JSObject>::cast(object);
   }
   if (caching_mode == CachingMode::kUnlimited ||

src/init/bootstrapper.cc

@@ -4599,8 +4599,9 @@ Handle<JSFunction> Genesis::CreateArrayBuffer(
 bool Genesis::InstallABunchOfRandomThings() {
   HandleScope scope(isolate());
 
-  auto fast_template_instantiations_cache = isolate()->factory()->NewFixedArray(
-      TemplateInfo::kFastTemplateInstantiationsCacheSize);
+  auto fast_template_instantiations_cache =
+      isolate()->factory()->NewFixedArrayWithHoles(
+          TemplateInfo::kFastTemplateInstantiationsCacheSize);
   native_context()->set_fast_template_instantiations_cache(
       *fast_template_instantiations_cache);