[embedder-tracing] Only expose GC call when used with --expose_gc

Bug: chromium:843903
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: Ie959e443fdf5dce92c4cd42ef62ec914a13b867e
Reviewed-on: https://chromium-review.googlesource.com/1187151
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55376}

src/api.cc

@@ -10456,7 +10456,8 @@ void EmbedderHeapTracer::FinalizeTracing() {
 
 void EmbedderHeapTracer::GarbageCollectionForTesting(
     EmbedderStackState stack_state) {
-  DCHECK(isolate_);
+  CHECK(isolate_);
+  CHECK(i::FLAG_expose_gc);
   i::Heap* const heap = reinterpret_cast<i::Isolate*>(isolate_)->heap();
   heap->SetEmbedderStackStateForNextFinalizaton(stack_state);
   heap->CollectAllGarbage(i::Heap::kAbortIncrementalMarkingMask,

test/cctest/heap/test-embedder-tracing.cc

@@ -253,6 +253,7 @@ TEST(FinalizeTracingWhenMarking) {
 
 TEST(GarbageCollectionForTesting) {
   ManualGCScope manual_gc;
+  i::FLAG_expose_gc = true;
   CcTest::InitializeVM();
   v8::Isolate* isolate = CcTest::isolate();
   Isolate* i_isolate = CcTest::i_isolate();