Use both object grouping and wrapper tracing.

To land and test wrapper tracing incrementally, we will use both, and parts
which are expected to work with the tracing will be removed from
V8GCController's handle visiting.

LOG=no
BUG=468240

Review URL: https://codereview.chromium.org/1925573002

Cr-Commit-Position: refs/heads/master@{#35809}

src/heap/mark-compact.cc

@@ -2051,7 +2051,8 @@ void MarkCompactCollector::ProcessEphemeralMarking(
     if (UsingEmbedderHeapTracer()) {
       embedder_heap_tracer()->TraceWrappersFrom(wrappers_to_trace_);
       wrappers_to_trace_.clear();
-    } else if (!only_process_harmony_weak_collections) {
+    }
+    if (!only_process_harmony_weak_collections) {
       isolate()->global_handles()->IterateObjectGroups(
           visitor, &IsUnmarkedHeapObjectWithHeap);
       MarkImplicitRefGroups(&MarkCompactMarkingVisitor::MarkObject);