[isolate] Fix CountUsage calls without a current native context

The blink use counter callback requires a current native context to
exist, and will crash if that is not the case. We can fix this V8 by
deferring the count. A cleaner (future) fix would be to either pass
the native context to the callback, or remove the requirement in
blink.

Bug: v8:9496,v8:10460
Change-Id: I8832d02088ba422c3a27638cee4dacbaaf6f39b4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2167394Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67421}

src/execution/isolate.cc

@@ -4249,9 +4249,15 @@ void Isolate::SetUseCounterCallback(v8::Isolate::UseCounterCallback callback) {
 }
 
 void Isolate::CountUsage(v8::Isolate::UseCounterFeature feature) {
-  // The counter callback may cause the embedder to call into V8, which is not
-  // generally possible during GC.
-  if (heap_.gc_state() == Heap::NOT_IN_GC) {
+  // The counter callback
+  // - may cause the embedder to call into V8, which is not generally possible
+  //   during GC.
+  // - requires a current native context, which may not always exist.
+  // TODO(jgruber): Consider either removing the native context requirement in
+  // blink, or passing it to the callback explicitly.
+  if (heap_.gc_state() == Heap::NOT_IN_GC && !context().is_null()) {
+    DCHECK(context().IsContext());
+    DCHECK(context().native_context().IsNativeContext());
     if (use_counter_callback_) {
       HandleScope handle_scope(this);
       use_counter_callback_(reinterpret_cast<v8::Isolate*>(this), feature);