GC: Add tracing event for rescanning large objects on newspace evacuation

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 6d3ceff7cb27567d1710c4e5c7b73553b6fb030b..57549f8036216d5bece3a06f1ff759bd3f859e18 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -3695,6 +3695,8 @@ void MarkCompactCollector::EvacuateNewSpaceAndCandidates() {
     }
 
     if (compacting_ && was_marked_incrementally_) {
+      GCTracer::Scope gc_scope(heap()->tracer(),
+                               GCTracer::Scope::MC_RESCAN_LARGE_OBJECTS);
       // It's difficult to filter out slots recorded for large objects.
       LargeObjectIterator it(heap_->lo_space());
       for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {