Introduce EmbedderHeapTracer::EnterFinalPause()

src/heap/mark-compact.cc

Index: src/heap/mark-compact.cc
diff --git a/src/heap/mark-compact.cc b/src/heap/mark-compact.cc
index 5c56fed9c99e11835b0c0f155dfca6dbeca00a1b..0c4c1a30cfcb6cff75b5911e15c43aaf04d7805b 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -869,6 +869,10 @@ void MarkCompactCollector::Prepare() {
     }
   }
 
+  if (UsingEmbedderHeapTracer()) {
+    embedder_heap_tracer()->EnterFinalPause();
+  }
+
   // Don't start compaction if we are in the middle of incremental
   // marking cycle. We did not collect any slots.
   if (!FLAG_never_compact && !was_marked_incrementally_) {