Use EmbedderHeapTracer instead of object grouping when trace_embedder_heap flag is set

src/flag-definitions.h

Index: src/flag-definitions.h
diff --git a/src/flag-definitions.h b/src/flag-definitions.h
index c1fffec8b878b6e49d89b1c7c912c05de7da7069..2d32068b65eba1719029ad572ce046903a8392c0 100644
--- a/src/flag-definitions.h
+++ b/src/flag-definitions.h
@@ -721,6 +721,10 @@ DEFINE_INT(histogram_interval, 600000,
 DEFINE_BOOL(trace_object_groups, false,
             "print object groups detected during each garbage collection")
 
+// heap.cc
+DEFINE_BOOL(trace_embedder_heap, false,
+            "use embedder heap tracing instead of object groups")
+
 // heap-snapshot-generator.cc
 DEFINE_BOOL(heap_profiler_trace_objects, false,
             "Dump heap object allocations/movements/size_updates")