Add GC request to libFuzzers in attempt to avoid parasitic coverage.

test/fuzzer/parser.cc

Index: test/fuzzer/parser.cc
diff --git a/test/fuzzer/parser.cc b/test/fuzzer/parser.cc
index be70b439efe45e76f01d663add1d103a4a1f75e6..4035adeaa3414ee020571a76d95368388e7fd6e2 100644
--- a/test/fuzzer/parser.cc
+++ b/test/fuzzer/parser.cc
@@ -38,5 +38,7 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
   info.set_global();
   v8::internal::Parser parser(&info);
   parser.Parse(&info);
+  isolate->RequestGarbageCollectionForTesting(
+      v8::Isolate::kFullGarbageCollection);
   return 0;
 }